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 $182.38   7.203%   $195.5168   $195.52   $195.50   $195.50  
  Purchase #2 $159.70   11.844%   $178.6149   $178.61   $178.60   $178.60  
  Purchase #3 $218.62   6.700%   $233.2675   $233.27   $233.25   $233.30  
  Purchase #4 $71.46   11.618%   $79.7622   $79.76   $79.75   $79.80  
  Purchase #5 $146.37   3.786%   $151.9116   $151.91   $151.90   $151.90  
  Purchase #6 $101.71   6.202%   $108.0181   $108.02   $108.00   $108.00  
  Purchase #7 $17.99   12.366%   $20.2146   $20.21   $20.20   $20.20  
  7 purchase totals = $898.23       $967.3057   $967.30   $967.20   $967.30