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 $172.32   9.239%   $188.2406   $188.24   $188.25   $188.20  
  Purchase #2 $182.62   3.564%   $189.1286   $189.13   $189.15   $189.10  
  Purchase #3 $166.61   5.478%   $175.7369   $175.74   $175.75   $175.70  
  Purchase #4 $103.39   13.496%   $117.3435   $117.34   $117.35   $117.30  
  Purchase #5 $154.97   11.469%   $172.7435   $172.74   $172.75   $172.70  
  Purchase #6 $200.45   13.631%   $227.7733   $227.77   $227.75   $227.80  
  Purchase #7 $214.40   3.486%   $221.874   $221.87   $221.85   $221.90  
  7 purchase totals = $1,194.76       $1,292.8404   $1,292.83   $1,292.85   $1,292.70