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 $248.36   5.141%   $261.1282   $261.13   $261.15   $261.10  
  Purchase #2 $47.74   3.419%   $49.3722   $49.37   $49.35   $49.40  
  Purchase #3 $29.49   13.142%   $33.3656   $33.37   $33.35   $33.40  
  Purchase #4 $64.62   3.447%   $66.8475   $66.85   $66.85   $66.80  
  Purchase #5 $59.76   11.565%   $66.6712   $66.67   $66.65   $66.70  
  Purchase #6 $204.45   9.636%   $224.1508   $224.15   $224.15   $224.20  
  Purchase #7 $241.42   8.167%   $261.1368   $261.14   $261.15   $261.10  
  7 purchase totals = $895.84       $962.6723   $962.68   $962.65   $962.70