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 $248.42   8.427%   $269.3544   $269.35   $269.35   $269.40  
  Purchase #2 $94.97   3.591%   $98.3804   $98.38   $98.40   $98.40  
  Purchase #3 $71.82   4.669%   $75.1733   $75.17   $75.15   $75.20  
  Purchase #4 $159.46   12.782%   $179.8422   $179.84   $179.85   $179.80  
  Purchase #5 $188.78   10.362%   $208.3414   $208.34   $208.35   $208.30  
  Purchase #6 $18.63   12.276%   $20.917   $20.92   $20.90   $20.90  
  Purchase #7 $82.58   10.155%   $90.966   $90.97   $90.95   $91.00  
  7 purchase totals = $864.66       $942.9747   $942.97   $942.95   $943.00