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 $108.69   9.142%   $118.6264   $118.63   $118.65   $118.60  
  Purchase #2 $17.87   10.647%   $19.7726   $19.77   $19.75   $19.80  
  Purchase #3 $247.92   5.545%   $261.6672   $261.67   $261.65   $261.70  
  Purchase #4 $131.98   10.539%   $145.8894   $145.89   $145.90   $145.90  
  Purchase #5 $127.36   10.731%   $141.027   $141.03   $141.05   $141.00  
  Purchase #6 $37.69   10.426%   $41.6196   $41.62   $41.60   $41.60  
  Purchase #7 $135.28   9.542%   $148.1884   $148.19   $148.20   $148.20  
  7 purchase totals = $806.79       $876.7906   $876.80   $876.80   $876.80