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 $197.61   3.870%   $205.2575   $205.26   $205.25   $205.30  
  Purchase #2 $72.93   13.302%   $82.6311   $82.63   $82.65   $82.60  
  Purchase #3 $215.45   5.599%   $227.513   $227.51   $227.50   $227.50  
  Purchase #4 $245.79   3.298%   $253.8962   $253.90   $253.90   $253.90  
  Purchase #5 $49.71   4.163%   $51.7794   $51.78   $51.80   $51.80  
  Purchase #6 $83.38   12.328%   $93.6591   $93.66   $93.65   $93.70  
  Purchase #7 $48.52   6.102%   $51.4807   $51.48   $51.50   $51.50  
  7 purchase totals = $913.39       $966.2170   $966.22   $966.25   $966.30