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 $45.86   8.282%   $49.6581   $49.66   $49.65   $49.70  
  Purchase #2 $85.56   10.628%   $94.6533   $94.65   $94.65   $94.70  
  Purchase #3 $68.99   7.766%   $74.3478   $74.35   $74.35   $74.30  
  Purchase #4 $64.97   5.533%   $68.5648   $68.56   $68.55   $68.60  
  Purchase #5 $209.55   12.670%   $236.1   $236.10   $236.10   $236.10  
  Purchase #6 $129.63   12.652%   $146.0308   $146.03   $146.05   $146.00  
  Purchase #7 $44.28   9.127%   $48.3214   $48.32   $48.30   $48.30  
  7 purchase totals = $648.84       $717.6762   $717.67   $717.65   $717.70