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 $55.75   11.136%   $61.9583   $61.96   $61.95   $62.00  
  Purchase #2 $234.79   11.571%   $261.9576   $261.96   $261.95   $262.00  
  Purchase #3 $233.80   9.749%   $256.5932   $256.59   $256.60   $256.60  
  Purchase #4 $154.59   10.441%   $170.7307   $170.73   $170.75   $170.70  
  Purchase #5 $244.97   6.582%   $261.0939   $261.09   $261.10   $261.10  
  Purchase #6 $37.79   8.754%   $41.0981   $41.10   $41.10   $41.10  
  Purchase #7 $241.55   3.220%   $249.3279   $249.33   $249.35   $249.30  
  7 purchase totals = $1,203.24       $1,302.7597   $1,302.76   $1,302.80   $1,302.80