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 $240.85   12.673%   $271.3729   $271.37   $271.35   $271.40  
  Purchase #2 $106.92   11.343%   $119.0479   $119.05   $119.05   $119.00  
  Purchase #3 $54.97   3.642%   $56.972   $56.97   $56.95   $57.00  
  Purchase #4 $164.26   13.731%   $186.8145   $186.81   $186.80   $186.80  
  Purchase #5 $132.26   3.712%   $137.1695   $137.17   $137.15   $137.20  
  Purchase #6 $93.25   10.713%   $103.2399   $103.24   $103.25   $103.20  
  Purchase #7 $62.86   10.366%   $69.3761   $69.38   $69.40   $69.40  
  7 purchase totals = $855.37       $943.9928   $943.99   $943.95   $944.00