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 $93.27   5.359%   $98.2683   $98.27   $98.25   $98.30  
  Purchase #2 $214.85   10.274%   $236.9237   $236.92   $236.90   $236.90  
  Purchase #3 $248.63   13.240%   $281.5486   $281.55   $281.55   $281.50  
  Purchase #4 $68.56   10.521%   $75.7732   $75.77   $75.75   $75.80  
  Purchase #5 $28.98   13.371%   $32.8549   $32.85   $32.85   $32.90  
  Purchase #6 $221.73   10.694%   $245.4418   $245.44   $245.45   $245.40  
  Purchase #7 $7.67   7.772%   $8.2661   $8.27   $8.25   $8.30  
  7 purchase totals = $883.69       $979.0766   $979.07   $979.00   $979.10