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 $144.37   6.243%   $153.383   $153.38   $153.40   $153.40  
  Purchase #2 $62.36   5.459%   $65.7642   $65.76   $65.75   $65.80  
  Purchase #3 $44.68   11.292%   $49.7253   $49.73   $49.75   $49.70  
  Purchase #4 $118.89   6.385%   $126.4811   $126.48   $126.50   $126.50  
  Purchase #5 $164.78   4.781%   $172.6581   $172.66   $172.65   $172.70  
  Purchase #6 $143.93   10.675%   $159.2945   $159.29   $159.30   $159.30  
  Purchase #7 $45.25   7.401%   $48.599   $48.60   $48.60   $48.60  
  7 purchase totals = $724.26       $775.9052   $775.90   $775.95   $776.00