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 $246.53   6.250%   $261.9381   $261.94   $261.95   $261.90  
  Purchase #2 $178.31   8.480%   $193.4307   $193.43   $193.45   $193.40  
  Purchase #3 $84.66   6.484%   $90.1494   $90.15   $90.15   $90.10  
  Purchase #4 $90.50   7.185%   $97.0024   $97.00   $97.00   $97.00  
  Purchase #5 $119.90   6.333%   $127.4933   $127.49   $127.50   $127.50  
  Purchase #6 $58.64   3.828%   $60.8847   $60.88   $60.90   $60.90  
  Purchase #7 $57.68   7.752%   $62.1514   $62.15   $62.15   $62.20  
  7 purchase totals = $836.22       $893.0500   $893.04   $893.10   $893.00