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 $123.69   10.789%   $137.0349   $137.03   $137.05   $137.00  
  Purchase #2 $48.89   3.284%   $50.4955   $50.50   $50.50   $50.50  
  Purchase #3 $187.47   11.823%   $209.6346   $209.63   $209.65   $209.60  
  Purchase #4 $95.33   8.773%   $103.6933   $103.69   $103.70   $103.70  
  Purchase #5 $131.64   8.207%   $142.4437   $142.44   $142.45   $142.40  
  Purchase #6 $98.97   7.378%   $106.272   $106.27   $106.25   $106.30  
  Purchase #7 $233.37   5.241%   $245.6009   $245.60   $245.60   $245.60  
  7 purchase totals = $919.36       $995.1749   $995.16   $995.20   $995.10