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 $60.62   8.184%   $65.5811   $65.58   $65.60   $65.60  
  Purchase #2 $35.60   4.478%   $37.1942   $37.19   $37.20   $37.20  
  Purchase #3 $127.26   7.341%   $136.6022   $136.60   $136.60   $136.60  
  Purchase #4 $189.62   13.763%   $215.7174   $215.72   $215.70   $215.70  
  Purchase #5 $129.29   10.347%   $142.6676   $142.67   $142.65   $142.70  
  Purchase #6 $51.81   10.611%   $57.3076   $57.31   $57.30   $57.30  
  Purchase #7 $233.64   8.448%   $253.3779   $253.38   $253.40   $253.40  
  7 purchase totals = $827.84       $908.4480   $908.45   $908.45   $908.50