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 $68.60   8.684%   $74.5572   $74.56   $74.55   $74.60  
  Purchase #2 $139.79   11.867%   $156.3789   $156.38   $156.40   $156.40  
  Purchase #3 $115.49   7.827%   $124.5294   $124.53   $124.55   $124.50  
  Purchase #4 $237.35   5.480%   $250.3568   $250.36   $250.35   $250.40  
  Purchase #5 $46.53   8.756%   $50.6042   $50.60   $50.60   $50.60  
  Purchase #6 $70.44   6.426%   $74.9665   $74.97   $74.95   $75.00  
  Purchase #7 $148.67   3.300%   $153.5761   $153.58   $153.60   $153.60  
  7 purchase totals = $826.87       $884.9691   $884.98   $885.00   $885.10