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 $206.92   8.385%   $224.2702   $224.27   $224.25   $224.30  
  Purchase #2 $26.61   13.853%   $30.2963   $30.30   $30.30   $30.30  
  Purchase #3 $57.99   8.236%   $62.7661   $62.77   $62.75   $62.80  
  Purchase #4 $170.85   6.684%   $182.2696   $182.27   $182.25   $182.30  
  Purchase #5 $39.51   7.633%   $42.5258   $42.53   $42.55   $42.50  
  Purchase #6 $114.65   7.457%   $123.1995   $123.20   $123.20   $123.20  
  Purchase #7 $88.44   11.253%   $98.3922   $98.39   $98.40   $98.40  
  7 purchase totals = $704.97       $763.7197   $763.73   $763.70   $763.80