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 $65.38   12.244%   $73.3851   $73.39   $73.40   $73.40  
  Purchase #2 $94.69   3.395%   $97.9047   $97.90   $97.90   $97.90  
  Purchase #3 $127.60   12.697%   $143.8014   $143.80   $143.80   $143.80  
  Purchase #4 $154.30   12.738%   $173.9547   $173.95   $173.95   $174.00  
  Purchase #5 $30.55   4.829%   $32.0253   $32.03   $32.05   $32.00  
  Purchase #6 $103.48   11.401%   $115.2778   $115.28   $115.30   $115.30  
  Purchase #7 $118.71   10.287%   $130.9217   $130.92   $130.90   $130.90  
  7 purchase totals = $694.71       $767.2707   $767.27   $767.30   $767.30