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 $221.50   5.158%   $232.925   $232.93   $232.95   $232.90  
  Purchase #2 $76.98   8.528%   $83.5449   $83.54   $83.55   $83.50  
  Purchase #3 $149.53   13.161%   $169.2096   $169.21   $169.20   $169.20  
  Purchase #4 $230.72   8.135%   $249.4891   $249.49   $249.50   $249.50  
  Purchase #5 $32.40   9.691%   $35.5399   $35.54   $35.55   $35.50  
  Purchase #6 $148.98   13.166%   $168.5947   $168.59   $168.60   $168.60  
  Purchase #7 $51.35   10.592%   $56.789   $56.79   $56.80   $56.80  
  7 purchase totals = $911.46       $996.0922   $996.09   $996.15   $996.00