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 $114.97   3.792%   $119.3297   $119.33   $119.35   $119.30  
  Purchase #2 $87.35   12.415%   $98.1945   $98.19   $98.20   $98.20  
  Purchase #3 $162.66   5.468%   $171.5542   $171.55   $171.55   $171.60  
  Purchase #4 $86.51   6.855%   $92.4403   $92.44   $92.45   $92.40  
  Purchase #5 $249.86   9.544%   $273.7066   $273.71   $273.70   $273.70  
  Purchase #6 $130.29   13.607%   $148.0186   $148.02   $148.00   $148.00  
  Purchase #7 $53.34   3.676%   $55.3008   $55.30   $55.30   $55.30  
  7 purchase totals = $884.98       $958.5447   $958.54   $958.55   $958.50