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 $119.48   4.590%   $124.9641   $124.96   $124.95   $125.00  
  Purchase #2 $229.68   5.416%   $242.1195   $242.12   $242.10   $242.10  
  Purchase #3 $105.56   8.460%   $114.4904   $114.49   $114.50   $114.50  
  Purchase #4 $202.26   13.163%   $228.8835   $228.88   $228.90   $228.90  
  Purchase #5 $131.25   9.393%   $143.5783   $143.58   $143.60   $143.60  
  Purchase #6 $138.92   5.528%   $146.5995   $146.60   $146.60   $146.60  
  Purchase #7 $162.97   10.377%   $179.8814   $179.88   $179.90   $179.90  
  7 purchase totals = $1,090.12       $1,180.5167   $1,180.51   $1,180.55   $1,180.60