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 $217.63   4.428%   $227.2667   $227.27   $227.25   $227.30  
  Purchase #2 $134.95   4.814%   $141.4465   $141.45   $141.45   $141.40  
  Purchase #3 $48.30   3.552%   $50.0156   $50.02   $50.00   $50.00  
  Purchase #4 $155.42   4.762%   $162.8211   $162.82   $162.80   $162.80  
  Purchase #5 $66.33   11.633%   $74.0462   $74.05   $74.05   $74.00  
  Purchase #6 $124.67   8.434%   $135.1847   $135.18   $135.20   $135.20  
  Purchase #7 $60.56   5.777%   $64.0586   $64.06   $64.05   $64.10  
  7 purchase totals = $807.86       $854.8394   $854.85   $854.80   $854.80