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 $194.39   12.716%   $219.1086   $219.11   $219.10   $219.10  
  Purchase #2 $57.77   11.840%   $64.61   $64.61   $64.60   $64.60  
  Purchase #3 $64.38   13.785%   $73.2548   $73.25   $73.25   $73.30  
  Purchase #4 $97.72   5.237%   $102.8376   $102.84   $102.85   $102.80  
  Purchase #5 $115.62   8.106%   $124.9922   $124.99   $125.00   $125.00  
  Purchase #6 $116.53   5.222%   $122.6152   $122.62   $122.60   $122.60  
  Purchase #7 $222.31   8.338%   $240.8462   $240.85   $240.85   $240.80  
  7 purchase totals = $868.72       $948.2646   $948.27   $948.25   $948.20