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 $61.55   7.686%   $66.2807   $66.28   $66.30   $66.30  
  Purchase #2 $183.88   10.842%   $203.8163   $203.82   $203.80   $203.80  
  Purchase #3 $92.93   11.792%   $103.8883   $103.89   $103.90   $103.90  
  Purchase #4 $235.26   12.804%   $265.3827   $265.38   $265.40   $265.40  
  Purchase #5 $137.40   10.593%   $151.9548   $151.95   $151.95   $152.00  
  Purchase #6 $178.73   13.223%   $202.3635   $202.36   $202.35   $202.40  
  Purchase #7 $191.45   12.315%   $215.0271   $215.03   $215.05   $215.00  
  7 purchase totals = $1,081.20       $1,208.7134   $1,208.71   $1,208.75   $1,208.80