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 $184.92   6.197%   $196.3795   $196.38   $196.40   $196.40  
  Purchase #2 $130.67   9.370%   $142.9138   $142.91   $142.90   $142.90  
  Purchase #3 $241.76   8.698%   $262.7883   $262.79   $262.80   $262.80  
  Purchase #4 $188.52   10.136%   $207.6284   $207.63   $207.65   $207.60  
  Purchase #5 $205.86   4.168%   $214.4402   $214.44   $214.45   $214.40  
  Purchase #6 $196.99   4.652%   $206.154   $206.15   $206.15   $206.20  
  Purchase #7 $125.73   10.547%   $138.9907   $138.99   $139.00   $139.00  
  7 purchase totals = $1,274.45       $1,369.2949   $1,369.29   $1,369.35   $1,369.30