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 $215.62   12.672%   $242.9434   $242.94   $242.95   $242.90  
  Purchase #2 $104.37   12.601%   $117.5217   $117.52   $117.50   $117.50  
  Purchase #3 $197.29   5.441%   $208.0245   $208.02   $208.00   $208.00  
  Purchase #4 $17.64   4.631%   $18.4569   $18.46   $18.45   $18.50  
  Purchase #5 $193.91   3.657%   $201.0013   $201.00   $201.00   $201.00  
  Purchase #6 $227.76   4.280%   $237.5081   $237.51   $237.50   $237.50  
  Purchase #7 $84.73   7.265%   $90.8856   $90.89   $90.90   $90.90  
  7 purchase totals = $1,041.32       $1,116.3415   $1,116.34   $1,116.30   $1,116.30