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 $14.95   12.733%   $16.8536   $16.85   $16.85   $16.90  
  Purchase #2 $125.29   7.533%   $134.7281   $134.73   $134.75   $134.70  
  Purchase #3 $142.82   7.202%   $153.1059   $153.11   $153.10   $153.10  
  Purchase #4 $226.69   4.119%   $236.0274   $236.03   $236.05   $236.00  
  Purchase #5 $143.54   8.868%   $156.2691   $156.27   $156.25   $156.30  
  Purchase #6 $230.97   4.132%   $240.5137   $240.51   $240.50   $240.50  
  Purchase #7 $105.96   3.226%   $109.3783   $109.38   $109.40   $109.40  
  7 purchase totals = $990.22       $1,046.8761   $1,046.88   $1,046.90   $1,046.90