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 $147.63   12.581%   $166.2033   $166.20   $166.20   $166.20  
  Purchase #2 $245.81   11.717%   $274.6116   $274.61   $274.60   $274.60  
  Purchase #3 $116.41   5.811%   $123.1746   $123.17   $123.15   $123.20  
  Purchase #4 $218.74   12.200%   $245.4263   $245.43   $245.45   $245.40  
  Purchase #5 $91.90   11.283%   $102.2691   $102.27   $102.25   $102.30  
  Purchase #6 $29.45   3.510%   $30.4837   $30.48   $30.50   $30.50  
  Purchase #7 $12.25   5.696%   $12.9478   $12.95   $12.95   $12.90  
  7 purchase totals = $862.19       $955.1164   $955.11   $955.10   $955.10