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 $70.27   13.698%   $79.8956   $79.90   $79.90   $79.90  
  Purchase #2 $13.41   9.139%   $14.6355   $14.64   $14.65   $14.60  
  Purchase #3 $111.29   8.488%   $120.7363   $120.74   $120.75   $120.70  
  Purchase #4 $61.29   13.725%   $69.7021   $69.70   $69.70   $69.70  
  Purchase #5 $32.63   5.637%   $34.4694   $34.47   $34.45   $34.50  
  Purchase #6 $204.91   4.648%   $214.4342   $214.43   $214.45   $214.40  
  Purchase #7 $78.98   4.338%   $82.4062   $82.41   $82.40   $82.40  
  7 purchase totals = $572.78       $616.2793   $616.29   $616.30   $616.20