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 $236.52   12.471%   $266.0164   $266.02   $266.00   $266.00  
  Purchase #2 $209.78   3.751%   $217.6488   $217.65   $217.65   $217.60  
  Purchase #3 $199.34   9.412%   $218.1019   $218.10   $218.10   $218.10  
  Purchase #4 $8.72   10.516%   $9.637   $9.64   $9.65   $9.60  
  Purchase #5 $14.30   10.231%   $15.763   $15.76   $15.75   $15.80  
  Purchase #6 $178.68   11.731%   $199.641   $199.64   $199.65   $199.60  
  Purchase #7 $212.42   6.337%   $225.8811   $225.88   $225.90   $225.90  
  7 purchase totals = $1,059.76       $1,152.6892   $1,152.69   $1,152.70   $1,152.60