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 $47.95   12.513%   $53.95   $53.95   $53.95   $54.00  
  Purchase #2 $125.32   12.164%   $140.5639   $140.56   $140.55   $140.60  
  Purchase #3 $48.63   9.196%   $53.102   $53.10   $53.10   $53.10  
  Purchase #4 $44.29   9.557%   $48.5228   $48.52   $48.50   $48.50  
  Purchase #5 $46.28   12.185%   $51.9192   $51.92   $51.90   $51.90  
  Purchase #6 $152.88   5.347%   $161.0545   $161.05   $161.05   $161.10  
  Purchase #7 $51.78   8.261%   $56.0575   $56.06   $56.05   $56.10  
  7 purchase totals = $517.13       $565.1699   $565.16   $565.10   $565.30