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 $82.80   11.619%   $92.4205   $92.42   $92.40   $92.40  
  Purchase #2 $227.82   9.615%   $249.7249   $249.72   $249.70   $249.70  
  Purchase #3 $28.90   11.629%   $32.2608   $32.26   $32.25   $32.30  
  Purchase #4 $173.75   9.663%   $190.5395   $190.54   $190.55   $190.50  
  Purchase #5 $125.87   7.726%   $135.5947   $135.59   $135.60   $135.60  
  Purchase #6 $158.55   7.492%   $170.4286   $170.43   $170.45   $170.40  
  Purchase #7 $176.28   10.593%   $194.9533   $194.95   $194.95   $195.00  
  7 purchase totals = $973.97       $1,065.9223   $1,065.91   $1,065.90   $1,065.90