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 $246.46   5.604%   $260.2716   $260.27   $260.25   $260.30  
  Purchase #2 $113.72   13.778%   $129.3883   $129.39   $129.40   $129.40  
  Purchase #3 $194.67   6.306%   $206.9459   $206.95   $206.95   $206.90  
  Purchase #4 $91.53   6.149%   $97.1582   $97.16   $97.15   $97.20  
  Purchase #5 $43.85   11.350%   $48.827   $48.83   $48.85   $48.80  
  Purchase #6 $54.41   9.794%   $59.7389   $59.74   $59.75   $59.70  
  Purchase #7 $211.42   11.250%   $235.2048   $235.20   $235.20   $235.20  
  7 purchase totals = $956.06       $1,037.5347   $1,037.54   $1,037.55   $1,037.50