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 $136.36   8.793%   $148.3501   $148.35   $148.35   $148.40  
  Purchase #2 $183.67   7.518%   $197.4783   $197.48   $197.50   $197.50  
  Purchase #3 $65.41   10.341%   $72.174   $72.17   $72.15   $72.20  
  Purchase #4 $11.28   8.829%   $12.2759   $12.28   $12.30   $12.30  
  Purchase #5 $132.42   11.718%   $147.937   $147.94   $147.95   $147.90  
  Purchase #6 $176.82   3.186%   $182.4535   $182.45   $182.45   $182.50  
  Purchase #7 $180.51   8.439%   $195.7432   $195.74   $195.75   $195.70  
  7 purchase totals = $886.47       $956.4120   $956.41   $956.45   $956.50