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 $115.83   8.815%   $126.0404   $126.04   $126.05   $126.00  
  Purchase #2 $74.95   13.362%   $84.9648   $84.96   $84.95   $85.00  
  Purchase #3 $64.26   3.686%   $66.6286   $66.63   $66.65   $66.60  
  Purchase #4 $40.94   13.482%   $46.4595   $46.46   $46.45   $46.50  
  Purchase #5 $245.73   6.296%   $261.2012   $261.20   $261.20   $261.20  
  Purchase #6 $193.34   8.775%   $210.3056   $210.31   $210.30   $210.30  
  Purchase #7 $95.71   4.408%   $99.9289   $99.93   $99.95   $99.90  
  7 purchase totals = $830.76       $895.5290   $895.53   $895.55   $895.50