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 $241.45   11.475%   $269.1564   $269.16   $269.15   $269.20  
  Purchase #2 $97.88   4.133%   $101.9254   $101.93   $101.95   $101.90  
  Purchase #3 $45.38   10.633%   $50.2053   $50.21   $50.20   $50.20  
  Purchase #4 $116.44   8.186%   $125.9718   $125.97   $125.95   $126.00  
  Purchase #5 $61.83   5.376%   $65.154   $65.15   $65.15   $65.20  
  Purchase #6 $153.75   12.759%   $173.367   $173.37   $173.35   $173.40  
  Purchase #7 $122.36   9.276%   $133.7101   $133.71   $133.70   $133.70  
  7 purchase totals = $839.09       $919.4900   $919.50   $919.45   $919.60