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 $60.76   7.279%   $65.1827   $65.18   $65.20   $65.20  
  Purchase #2 $98.62   13.177%   $111.6152   $111.62   $111.60   $111.60  
  Purchase #3 $63.91   13.447%   $72.504   $72.50   $72.50   $72.50  
  Purchase #4 $5.97   6.463%   $6.3558   $6.36   $6.35   $6.40  
  Purchase #5 $13.80   4.737%   $14.4537   $14.45   $14.45   $14.50  
  Purchase #6 $148.63   6.714%   $158.609   $158.61   $158.60   $158.60  
  Purchase #7 $153.30   8.432%   $166.2263   $166.23   $166.25   $166.20  
  7 purchase totals = $544.99       $594.9467   $594.95   $594.95   $595.00