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 $65.64   11.874%   $73.4341   $73.43   $73.45   $73.40  
  Purchase #2 $104.63   5.706%   $110.6002   $110.60   $110.60   $110.60  
  Purchase #3 $13.41   11.167%   $14.9075   $14.91   $14.90   $14.90  
  Purchase #4 $243.80   7.297%   $261.5901   $261.59   $261.60   $261.60  
  Purchase #5 $152.62   10.485%   $168.6222   $168.62   $168.60   $168.60  
  Purchase #6 $158.61   12.505%   $178.4442   $178.44   $178.45   $178.40  
  Purchase #7 $151.42   5.619%   $159.9283   $159.93   $159.95   $159.90  
  7 purchase totals = $890.13       $967.5266   $967.52   $967.55   $967.40