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 $121.74   9.526%   $133.337   $133.34   $133.35   $133.30  
  Purchase #2 $23.51   4.671%   $24.6082   $24.61   $24.60   $24.60  
  Purchase #3 $9.68   9.832%   $10.6317   $10.63   $10.65   $10.60  
  Purchase #4 $86.31   7.301%   $92.6115   $92.61   $92.60   $92.60  
  Purchase #5 $53.25   8.430%   $57.739   $57.74   $57.75   $57.70  
  Purchase #6 $204.48   8.503%   $221.8669   $221.87   $221.85   $221.90  
  Purchase #7 $123.57   10.666%   $136.75   $136.75   $136.75   $136.80  
  7 purchase totals = $622.54       $677.5443   $677.55   $677.55   $677.50