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 $241.51   8.259%   $261.4563   $261.46   $261.45   $261.50  
  Purchase #2 $142.84   11.507%   $159.2766   $159.28   $159.30   $159.30  
  Purchase #3 $162.82   3.128%   $167.913   $167.91   $167.90   $167.90  
  Purchase #4 $13.62   11.380%   $15.17   $15.17   $15.15   $15.20  
  Purchase #5 $74.50   12.506%   $83.817   $83.82   $83.80   $83.80  
  Purchase #6 $127.85   13.108%   $144.6086   $144.61   $144.60   $144.60  
  Purchase #7 $85.87   9.481%   $94.0113   $94.01   $94.00   $94.00  
  7 purchase totals = $849.01       $926.2528   $926.26   $926.20   $926.30