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 $227.65   11.380%   $253.5566   $253.56   $253.55   $253.60  
  Purchase #2 $212.45   4.324%   $221.6363   $221.64   $221.65   $221.60  
  Purchase #3 $53.41   5.274%   $56.2268   $56.23   $56.25   $56.20  
  Purchase #4 $92.36   9.831%   $101.4399   $101.44   $101.45   $101.40  
  Purchase #5 $89.50   8.740%   $97.3223   $97.32   $97.30   $97.30  
  Purchase #6 $190.46   9.498%   $208.5499   $208.55   $208.55   $208.50  
  Purchase #7 $17.26   6.188%   $18.328   $18.33   $18.35   $18.30  
  7 purchase totals = $883.09       $957.0598   $957.07   $957.10   $956.90