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 $14.95   6.779%   $15.9635   $15.96   $15.95   $16.00  
  Purchase #2 $168.52   4.559%   $176.2028   $176.20   $176.20   $176.20  
  Purchase #3 $125.29   6.621%   $133.5855   $133.59   $133.60   $133.60  
  Purchase #4 $144.91   13.305%   $164.1903   $164.19   $164.20   $164.20  
  Purchase #5 $26.27   3.106%   $27.0859   $27.09   $27.10   $27.10  
  Purchase #6 $170.71   8.353%   $184.9694   $184.97   $184.95   $185.00  
  Purchase #7 $119.50   13.695%   $135.8655   $135.87   $135.85   $135.90  
  7 purchase totals = $770.15       $837.8629   $837.87   $837.85   $838.00