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 $36.67   3.382%   $37.9102   $37.91   $37.90   $37.90  
  Purchase #2 $44.46   8.259%   $48.132   $48.13   $48.15   $48.10  
  Purchase #3 $24.26   6.156%   $25.7534   $25.75   $25.75   $25.80  
  Purchase #4 $72.35   5.738%   $76.5014   $76.50   $76.50   $76.50  
  Purchase #5 $146.83   3.628%   $152.157   $152.16   $152.15   $152.20  
  Purchase #6 $166.55   8.290%   $180.357   $180.36   $180.35   $180.40  
  Purchase #7 $209.69   3.116%   $216.2239   $216.22   $216.20   $216.20  
  7 purchase totals = $700.81       $737.0349   $737.03   $737.00   $737.10