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 $117.35   10.451%   $129.6142   $129.61   $129.60   $129.60  
  Purchase #2 $11.64   5.143%   $12.2386   $12.24   $12.25   $12.20  
  Purchase #3 $44.62   10.799%   $49.4385   $49.44   $49.45   $49.40  
  Purchase #4 $127.48   3.849%   $132.3867   $132.39   $132.40   $132.40  
  Purchase #5 $176.30   7.558%   $189.6248   $189.62   $189.60   $189.60  
  Purchase #6 $15.60   10.353%   $17.2151   $17.22   $17.20   $17.20  
  Purchase #7 $20.67   8.810%   $22.491   $22.49   $22.50   $22.50  
  7 purchase totals = $513.66       $553.0089   $553.01   $553.00   $552.90