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 $238.29   12.113%   $267.1541   $267.15   $267.15   $267.20  
  Purchase #2 $154.62   12.287%   $173.6182   $173.62   $173.60   $173.60  
  Purchase #3 $117.95   12.660%   $132.8825   $132.88   $132.90   $132.90  
  Purchase #4 $70.43   8.383%   $76.3341   $76.33   $76.35   $76.30  
  Purchase #5 $55.71   7.126%   $59.6799   $59.68   $59.70   $59.70  
  Purchase #6 $154.25   9.446%   $168.8205   $168.82   $168.80   $168.80  
  Purchase #7 $220.98   11.213%   $245.7585   $245.76   $245.75   $245.80  
  7 purchase totals = $1,012.23       $1,124.2478   $1,124.24   $1,124.25   $1,124.30