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 $61.67   9.137%   $67.3048   $67.30   $67.30   $67.30  
  Purchase #2 $187.97   8.644%   $204.2181   $204.22   $204.20   $204.20  
  Purchase #3 $12.76   11.530%   $14.2312   $14.23   $14.25   $14.20  
  Purchase #4 $224.31   10.447%   $247.7437   $247.74   $247.75   $247.70  
  Purchase #5 $95.91   4.142%   $99.8826   $99.88   $99.90   $99.90  
  Purchase #6 $215.83   10.139%   $237.713   $237.71   $237.70   $237.70  
  Purchase #7 $103.81   12.403%   $116.6856   $116.69   $116.70   $116.70  
  7 purchase totals = $902.26       $987.7790   $987.77   $987.80   $987.70