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 $237.54   9.272%   $259.5647   $259.56   $259.55   $259.60  
  Purchase #2 $216.93   10.723%   $240.1914   $240.19   $240.20   $240.20  
  Purchase #3 $203.91   9.288%   $222.8492   $222.85   $222.85   $222.80  
  Purchase #4 $239.65   8.734%   $260.581   $260.58   $260.60   $260.60  
  Purchase #5 $178.62   5.232%   $187.9654   $187.97   $187.95   $188.00  
  Purchase #6 $62.30   4.578%   $65.1521   $65.15   $65.15   $65.20  
  Purchase #7 $238.46   7.149%   $255.5075   $255.51   $255.50   $255.50  
  7 purchase totals = $1,377.41       $1,491.8113   $1,491.81   $1,491.80   $1,491.90