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 $216.47   11.594%   $241.5675   $241.57   $241.55   $241.60  
  Purchase #2 $49.93   6.556%   $53.2034   $53.20   $53.20   $53.20  
  Purchase #3 $146.45   7.234%   $157.0442   $157.04   $157.05   $157.00  
  Purchase #4 $160.49   6.174%   $170.3987   $170.40   $170.40   $170.40  
  Purchase #5 $92.30   4.161%   $96.1406   $96.14   $96.15   $96.10  
  Purchase #6 $78.38   12.204%   $87.9455   $87.95   $87.95   $87.90  
  Purchase #7 $170.35   6.860%   $182.036   $182.04   $182.05   $182.00  
  7 purchase totals = $914.37       $988.3359   $988.34   $988.35   $988.20