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 $62.87   4.818%   $65.8991   $65.90   $65.90   $65.90  
  Purchase #2 $161.68   9.170%   $176.5061   $176.51   $176.50   $176.50  
  Purchase #3 $222.99   4.564%   $233.1673   $233.17   $233.15   $233.20  
  Purchase #4 $155.54   13.316%   $176.2517   $176.25   $176.25   $176.30  
  Purchase #5 $124.73   10.536%   $137.8716   $137.87   $137.85   $137.90  
  Purchase #6 $65.97   13.574%   $74.9248   $74.92   $74.90   $74.90  
  Purchase #7 $152.69   10.503%   $168.727   $168.73   $168.75   $168.70  
  7 purchase totals = $946.47       $1,033.3476   $1,033.35   $1,033.30   $1,033.40