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 $61.27   8.714%   $66.6091   $66.61   $66.60   $66.60  
  Purchase #2 $14.92   12.218%   $16.7429   $16.74   $16.75   $16.70  
  Purchase #3 $225.92   6.587%   $240.8014   $240.80   $240.80   $240.80  
  Purchase #4 $98.83   12.506%   $111.1897   $111.19   $111.20   $111.20  
  Purchase #5 $59.27   12.361%   $66.5964   $66.60   $66.60   $66.60  
  Purchase #6 $242.27   4.481%   $253.1261   $253.13   $253.15   $253.10  
  Purchase #7 $205.91   13.622%   $233.9591   $233.96   $233.95   $234.00  
  7 purchase totals = $908.39       $989.0247   $989.03   $989.05   $989.00