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 $59.84   12.310%   $67.2063   $67.21   $67.20   $67.20  
  Purchase #2 $182.75   5.240%   $192.3261   $192.33   $192.35   $192.30  
  Purchase #3 $131.74   6.839%   $140.7497   $140.75   $140.75   $140.70  
  Purchase #4 $115.85   13.188%   $131.1283   $131.13   $131.15   $131.10  
  Purchase #5 $30.75   8.354%   $33.3189   $33.32   $33.30   $33.30  
  Purchase #6 $116.56   13.871%   $132.728   $132.73   $132.75   $132.70  
  Purchase #7 $233.58   4.562%   $244.2359   $244.24   $244.25   $244.20  
  7 purchase totals = $871.07       $941.6932   $941.71   $941.75   $941.50