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 $37.59   10.456%   $41.5204   $41.52   $41.50   $41.50  
  Purchase #2 $225.65   5.140%   $237.2484   $237.25   $237.25   $237.20  
  Purchase #3 $206.82   8.531%   $224.4638   $224.46   $224.45   $224.50  
  Purchase #4 $15.63   6.323%   $16.6183   $16.62   $16.60   $16.60  
  Purchase #5 $84.25   6.517%   $89.7406   $89.74   $89.75   $89.70  
  Purchase #6 $97.42   4.252%   $101.5623   $101.56   $101.55   $101.60  
  Purchase #7 $93.90   11.256%   $104.4694   $104.47   $104.45   $104.50  
  7 purchase totals = $761.26       $815.6232   $815.62   $815.55   $815.60