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 $215.98   3.829%   $224.2499   $224.25   $224.25   $224.20  
  Purchase #2 $158.83   11.284%   $176.7524   $176.75   $176.75   $176.80  
  Purchase #3 $68.60   7.720%   $73.8959   $73.90   $73.90   $73.90  
  Purchase #4 $154.51   11.795%   $172.7345   $172.73   $172.75   $172.70  
  Purchase #5 $42.77   10.735%   $47.3614   $47.36   $47.35   $47.40  
  Purchase #6 $198.36   12.347%   $222.8515   $222.85   $222.85   $222.90  
  Purchase #7 $240.71   10.631%   $266.2999   $266.30   $266.30   $266.30  
  7 purchase totals = $1,079.76       $1,184.1455   $1,184.14   $1,184.15   $1,184.20