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 $204.67   13.644%   $232.5952   $232.60   $232.60   $232.60  
  Purchase #2 $230.42   8.244%   $249.4158   $249.42   $249.40   $249.40  
  Purchase #3 $179.84   7.838%   $193.9359   $193.94   $193.95   $193.90  
  Purchase #4 $201.61   3.778%   $209.2268   $209.23   $209.25   $209.20  
  Purchase #5 $125.51   12.472%   $141.1636   $141.16   $141.15   $141.20  
  Purchase #6 $204.53   10.106%   $225.1998   $225.20   $225.20   $225.20  
  Purchase #7 $173.67   13.867%   $197.7528   $197.75   $197.75   $197.80  
  7 purchase totals = $1,320.25       $1,449.2899   $1,449.30   $1,449.30   $1,449.30