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 $77.98   8.355%   $84.4952   $84.50   $84.50   $84.50  
  Purchase #2 $115.26   7.775%   $124.2215   $124.22   $124.20   $124.20  
  Purchase #3 $57.69   13.344%   $65.3882   $65.39   $65.40   $65.40  
  Purchase #4 $182.28   7.839%   $196.5689   $196.57   $196.55   $196.60  
  Purchase #5 $59.60   7.733%   $64.2089   $64.21   $64.20   $64.20  
  Purchase #6 $240.34   4.385%   $250.8789   $250.88   $250.90   $250.90  
  Purchase #7 $210.93   10.741%   $233.586   $233.59   $233.60   $233.60  
  7 purchase totals = $944.08       $1,019.3476   $1,019.36   $1,019.35   $1,019.40