Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.98   11.794%   $239.2168   $239.22   $239.20   $239.20  
  Purchase #2 $102.94   10.395%   $113.6406   $113.64   $113.65   $113.60  
  Purchase #3 $199.80   4.863%   $209.5163   $209.52   $209.50   $209.50  
  Purchase #4 $169.86   4.335%   $177.2234   $177.22   $177.20   $177.20  
  Purchase #5 $211.45   11.251%   $235.2402   $235.24   $235.25   $235.20  
  Purchase #6 $196.37   9.154%   $214.3457   $214.35   $214.35   $214.30  
  Purchase #7 $154.89   10.815%   $171.6414   $171.64   $171.65   $171.60  
  7 purchase totals = $1,249.29       $1,360.8244   $1,360.83   $1,360.80   $1,360.60