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 $241.68   8.398%   $261.9763   $261.98   $262.00   $262.00  
  Purchase #2 $44.66   5.740%   $47.2235   $47.22   $47.20   $47.20  
  Purchase #3 $114.37   11.344%   $127.3441   $127.34   $127.35   $127.30  
  Purchase #4 $66.92   8.174%   $72.39   $72.39   $72.40   $72.40  
  Purchase #5 $232.63   13.713%   $264.5306   $264.53   $264.55   $264.50  
  Purchase #6 $65.59   5.197%   $68.9987   $69.00   $69.00   $69.00  
  Purchase #7 $91.64   7.717%   $98.7119   $98.71   $98.70   $98.70  
  7 purchase totals = $857.49       $941.1751   $941.17   $941.20   $941.10