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 $92.38   9.534%   $101.1875   $101.19   $101.20   $101.20  
  Purchase #2 $209.85   13.364%   $237.8944   $237.89   $237.90   $237.90  
  Purchase #3 $111.76   5.190%   $117.5603   $117.56   $117.55   $117.60  
  Purchase #4 $198.40   5.513%   $209.3378   $209.34   $209.35   $209.30  
  Purchase #5 $239.30   7.329%   $256.8383   $256.84   $256.85   $256.80  
  Purchase #6 $146.95   3.683%   $152.3622   $152.36   $152.35   $152.40  
  Purchase #7 $141.73   6.642%   $151.1437   $151.14   $151.15   $151.10  
  7 purchase totals = $1,140.37       $1,226.3242   $1,226.32   $1,226.35   $1,226.30