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 $173.93   12.536%   $195.7339   $195.73   $195.75   $195.70  
  Purchase #2 $243.91   9.328%   $266.6619   $266.66   $266.65   $266.70  
  Purchase #3 $75.60   11.849%   $84.5578   $84.56   $84.55   $84.60  
  Purchase #4 $201.54   11.338%   $224.3906   $224.39   $224.40   $224.40  
  Purchase #5 $199.41   9.425%   $218.2044   $218.20   $218.20   $218.20  
  Purchase #6 $124.65   4.382%   $130.1122   $130.11   $130.10   $130.10  
  Purchase #7 $190.30   9.538%   $208.4508   $208.45   $208.45   $208.50  
  7 purchase totals = $1,209.34       $1,328.1116   $1,328.10   $1,328.10   $1,328.20