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 $234.98   11.197%   $261.2907   $261.29   $261.30   $261.30  
  Purchase #2 $146.95   8.496%   $159.4349   $159.43   $159.45   $159.40  
  Purchase #3 $173.91   13.521%   $197.4244   $197.42   $197.40   $197.40  
  Purchase #4 $63.37   7.201%   $67.9333   $67.93   $67.95   $67.90  
  Purchase #5 $48.52   5.261%   $51.0726   $51.07   $51.05   $51.10  
  Purchase #6 $119.88   13.275%   $135.7941   $135.79   $135.80   $135.80  
  Purchase #7 $142.69   6.237%   $151.5896   $151.59   $151.60   $151.60  
  7 purchase totals = $930.30       $1,024.5396   $1,024.52   $1,024.55   $1,024.50