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 $108.35   10.385%   $119.6021   $119.60   $119.60   $119.60  
  Purchase #2 $157.37   3.176%   $162.3681   $162.37   $162.35   $162.40  
  Purchase #3 $248.39   11.361%   $276.6096   $276.61   $276.60   $276.60  
  Purchase #4 $156.60   7.367%   $168.1367   $168.14   $168.15   $168.10  
  Purchase #5 $25.57   5.345%   $26.9367   $26.94   $26.95   $26.90  
  Purchase #6 $195.52   9.423%   $213.9438   $213.94   $213.95   $213.90  
  Purchase #7 $34.36   7.179%   $36.8267   $36.83   $36.85   $36.80  
  7 purchase totals = $926.16       $1,004.4237   $1,004.43   $1,004.45   $1,004.30