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 $198.63   5.602%   $209.7573   $209.76   $209.75   $209.80  
  Purchase #2 $24.61   13.353%   $27.8962   $27.90   $27.90   $27.90  
  Purchase #3 $143.93   12.620%   $162.094   $162.09   $162.10   $162.10  
  Purchase #4 $131.95   9.759%   $144.827   $144.83   $144.85   $144.80  
  Purchase #5 $72.26   4.533%   $75.5355   $75.54   $75.55   $75.50  
  Purchase #6 $49.65   3.230%   $51.2537   $51.25   $51.25   $51.30  
  Purchase #7 $76.43   11.162%   $84.9611   $84.96   $84.95   $85.00  
  7 purchase totals = $697.46       $756.3248   $756.33   $756.35   $756.40