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 $109.59   8.812%   $119.2471   $119.25   $119.25   $119.20  
  Purchase #2 $98.93   5.426%   $104.2979   $104.30   $104.30   $104.30  
  Purchase #3 $170.35   13.521%   $193.383   $193.38   $193.40   $193.40  
  Purchase #4 $240.45   6.868%   $256.9641   $256.96   $256.95   $257.00  
  Purchase #5 $53.81   12.868%   $60.7343   $60.73   $60.75   $60.70  
  Purchase #6 $171.45   13.766%   $195.0518   $195.05   $195.05   $195.10  
  Purchase #7 $233.92   3.281%   $241.5949   $241.59   $241.60   $241.60  
  7 purchase totals = $1,078.50       $1,171.2731   $1,171.26   $1,171.30   $1,171.30