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 $34.57   5.825%   $36.5837   $36.58   $36.60   $36.60  
  Purchase #2 $73.71   10.427%   $81.3957   $81.40   $81.40   $81.40  
  Purchase #3 $20.29   4.826%   $21.2692   $21.27   $21.25   $21.30  
  Purchase #4 $46.74   9.592%   $51.2233   $51.22   $51.20   $51.20  
  Purchase #5 $244.62   4.600%   $255.8725   $255.87   $255.85   $255.90  
  Purchase #6 $142.96   7.233%   $153.3003   $153.30   $153.30   $153.30  
  Purchase #7 $184.91   5.255%   $194.627   $194.63   $194.65   $194.60  
  7 purchase totals = $747.80       $794.2717   $794.27   $794.25   $794.30