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 $208.65   13.466%   $236.7468   $236.75   $236.75   $236.70  
  Purchase #2 $82.81   11.503%   $92.3356   $92.34   $92.35   $92.30  
  Purchase #3 $76.46   11.669%   $85.3821   $85.38   $85.40   $85.40  
  Purchase #4 $168.61   7.202%   $180.7533   $180.75   $180.75   $180.80  
  Purchase #5 $207.54   13.105%   $234.7381   $234.74   $234.75   $234.70  
  Purchase #6 $88.68   6.337%   $94.2997   $94.30   $94.30   $94.30  
  Purchase #7 $37.26   6.507%   $39.6845   $39.68   $39.70   $39.70  
  7 purchase totals = $870.01       $963.9401   $963.94   $964.00   $963.90