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 $111.92   6.616%   $119.3246   $119.32   $119.30   $119.30  
  Purchase #2 $61.47   5.359%   $64.7642   $64.76   $64.75   $64.80  
  Purchase #3 $167.73   3.468%   $173.5469   $173.55   $173.55   $173.50  
  Purchase #4 $12.73   7.682%   $13.7079   $13.71   $13.70   $13.70  
  Purchase #5 $77.75   6.381%   $82.7112   $82.71   $82.70   $82.70  
  Purchase #6 $176.25   3.432%   $182.2989   $182.30   $182.30   $182.30  
  Purchase #7 $60.68   6.506%   $64.6278   $64.63   $64.65   $64.60  
  7 purchase totals = $668.53       $700.9815   $700.98   $700.95   $700.90