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 $24.43   13.116%   $27.6342   $27.63   $27.65   $27.60  
  Purchase #2 $95.49   12.264%   $107.2009   $107.20   $107.20   $107.20  
  Purchase #3 $93.36   7.646%   $100.4983   $100.50   $100.50   $100.50  
  Purchase #4 $46.48   11.748%   $51.9405   $51.94   $51.95   $51.90  
  Purchase #5 $167.53   4.864%   $175.6787   $175.68   $175.70   $175.70  
  Purchase #6 $236.67   9.117%   $258.2472   $258.25   $258.25   $258.20  
  Purchase #7 $209.33   8.804%   $227.7594   $227.76   $227.75   $227.80  
  7 purchase totals = $873.29       $948.9592   $948.96   $949.00   $948.90