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 $104.51   9.841%   $114.7948   $114.79   $114.80   $114.80  
  Purchase #2 $211.47   8.304%   $229.0305   $229.03   $229.05   $229.00  
  Purchase #3 $174.93   4.334%   $182.5115   $182.51   $182.50   $182.50  
  Purchase #4 $89.45   9.325%   $97.7912   $97.79   $97.80   $97.80  
  Purchase #5 $206.51   4.839%   $216.503   $216.50   $216.50   $216.50  
  Purchase #6 $155.92   3.697%   $161.6844   $161.68   $161.70   $161.70  
  Purchase #7 $14.48   7.126%   $15.5118   $15.51   $15.50   $15.50  
  7 purchase totals = $957.27       $1,017.8272   $1,017.81   $1,017.85   $1,017.80