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 $202.78   10.559%   $224.1915   $224.19   $224.20   $224.20  
  Purchase #2 $164.34   5.451%   $173.2982   $173.30   $173.30   $173.30  
  Purchase #3 $66.29   10.715%   $73.393   $73.39   $73.40   $73.40  
  Purchase #4 $105.67   11.617%   $117.9457   $117.95   $117.95   $117.90  
  Purchase #5 $148.72   3.801%   $154.3728   $154.37   $154.35   $154.40  
  Purchase #6 $148.80   9.585%   $163.0625   $163.06   $163.05   $163.10  
  Purchase #7 $49.47   4.513%   $51.7026   $51.70   $51.70   $51.70  
  7 purchase totals = $886.07       $957.9663   $957.96   $957.95   $958.00