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 $62.86   12.465%   $70.6955   $70.70   $70.70   $70.70  
  Purchase #2 $223.35   11.613%   $249.2876   $249.29   $249.30   $249.30  
  Purchase #3 $214.51   4.601%   $224.3796   $224.38   $224.40   $224.40  
  Purchase #4 $78.99   3.301%   $81.5975   $81.60   $81.60   $81.60  
  Purchase #5 $153.75   3.510%   $159.1466   $159.15   $159.15   $159.10  
  Purchase #6 $245.68   7.226%   $263.4328   $263.43   $263.45   $263.40  
  Purchase #7 $72.43   5.304%   $76.2717   $76.27   $76.25   $76.30  
  7 purchase totals = $1,051.57       $1,124.8113   $1,124.82   $1,124.85   $1,124.80