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 $119.36   11.874%   $133.5328   $133.53   $133.55   $133.50  
  Purchase #2 $72.25   6.113%   $76.6666   $76.67   $76.65   $76.70  
  Purchase #3 $49.43   5.463%   $52.1304   $52.13   $52.15   $52.10  
  Purchase #4 $63.91   4.681%   $66.9016   $66.90   $66.90   $66.90  
  Purchase #5 $75.76   10.865%   $83.9913   $83.99   $84.00   $84.00  
  Purchase #6 $244.81   3.372%   $253.065   $253.07   $253.05   $253.10  
  Purchase #7 $84.50   8.126%   $91.3665   $91.37   $91.35   $91.40  
  7 purchase totals = $710.02       $757.6542   $757.66   $757.65   $757.70