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 $57.67   11.570%   $64.3424   $64.34   $64.35   $64.30  
  Purchase #2 $42.79   11.420%   $47.6766   $47.68   $47.70   $47.70  
  Purchase #3 $98.95   12.108%   $110.9309   $110.93   $110.95   $110.90  
  Purchase #4 $206.55   12.689%   $232.7591   $232.76   $232.75   $232.80  
  Purchase #5 $59.27   3.135%   $61.1281   $61.13   $61.15   $61.10  
  Purchase #6 $168.83   12.867%   $190.5534   $190.55   $190.55   $190.60  
  Purchase #7 $210.26   8.197%   $227.495   $227.50   $227.50   $227.50  
  7 purchase totals = $844.32       $934.8855   $934.89   $934.95   $934.90