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 $208.98   10.658%   $231.2531   $231.25   $231.25   $231.30  
  Purchase #2 $49.44   4.631%   $51.7296   $51.73   $51.75   $51.70  
  Purchase #3 $131.70   7.723%   $141.8712   $141.87   $141.85   $141.90  
  Purchase #4 $75.87   13.630%   $86.2111   $86.21   $86.20   $86.20  
  Purchase #5 $156.65   5.768%   $165.6856   $165.69   $165.70   $165.70  
  Purchase #6 $244.89   8.616%   $265.9897   $265.99   $266.00   $266.00  
  Purchase #7 $119.90   12.785%   $135.2292   $135.23   $135.25   $135.20  
  7 purchase totals = $987.43       $1,077.9695   $1,077.97   $1,078.00   $1,078.00