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 $250.56   4.193%   $261.066   $261.07   $261.05   $261.10  
  Purchase #2 $230.65   11.206%   $256.4966   $256.50   $256.50   $256.50  
  Purchase #3 $195.38   3.807%   $202.8181   $202.82   $202.80   $202.80  
  Purchase #4 $221.57   9.474%   $242.5615   $242.56   $242.55   $242.60  
  Purchase #5 $119.43   4.790%   $125.1507   $125.15   $125.15   $125.20  
  Purchase #6 $5.97   13.302%   $6.7641   $6.76   $6.75   $6.80  
  Purchase #7 $50.56   10.754%   $55.9972   $56.00   $56.00   $56.00  
  7 purchase totals = $1,074.12       $1,150.8542   $1,150.86   $1,150.80   $1,151.00