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 $60.54   8.600%   $65.7464   $65.75   $65.75   $65.70  
  Purchase #2 $249.86   11.135%   $277.6819   $277.68   $277.70   $277.70  
  Purchase #3 $186.93   6.822%   $199.6824   $199.68   $199.70   $199.70  
  Purchase #4 $173.25   5.724%   $183.1668   $183.17   $183.15   $183.20  
  Purchase #5 $200.91   7.397%   $215.7713   $215.77   $215.75   $215.80  
  Purchase #6 $8.57   8.764%   $9.3211   $9.32   $9.30   $9.30  
  Purchase #7 $76.91   9.511%   $84.2249   $84.22   $84.20   $84.20  
  7 purchase totals = $956.97       $1,035.5948   $1,035.59   $1,035.55   $1,035.60