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 $202.49   12.475%   $227.7506   $227.75   $227.75   $227.80  
  Purchase #2 $114.66   4.523%   $119.8461   $119.85   $119.85   $119.80  
  Purchase #3 $168.55   12.812%   $190.1446   $190.14   $190.15   $190.10  
  Purchase #4 $47.25   8.423%   $51.2299   $51.23   $51.25   $51.20  
  Purchase #5 $8.68   9.574%   $9.511   $9.51   $9.50   $9.50  
  Purchase #6 $14.52   4.730%   $15.2068   $15.21   $15.20   $15.20  
  Purchase #7 $135.75   9.464%   $148.5974   $148.60   $148.60   $148.60  
  7 purchase totals = $691.90       $762.2864   $762.29   $762.30   $762.20