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 $182.46   11.450%   $203.3517   $203.35   $203.35   $203.40  
  Purchase #2 $56.68   13.143%   $64.1295   $64.13   $64.15   $64.10  
  Purchase #3 $112.85   4.306%   $117.7093   $117.71   $117.70   $117.70  
  Purchase #4 $16.49   5.543%   $17.404   $17.40   $17.40   $17.40  
  Purchase #5 $232.70   12.283%   $261.2825   $261.28   $261.30   $261.30  
  Purchase #6 $81.86   4.490%   $85.5355   $85.54   $85.55   $85.50  
  Purchase #7 $166.89   13.376%   $189.2132   $189.21   $189.20   $189.20  
  7 purchase totals = $849.93       $938.6257   $938.62   $938.65   $938.60