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 $192.34   7.153%   $206.0981   $206.10   $206.10   $206.10  
  Purchase #2 $208.63   3.485%   $215.9008   $215.90   $215.90   $215.90  
  Purchase #3 $39.58   7.844%   $42.6847   $42.68   $42.70   $42.70  
  Purchase #4 $104.54   12.214%   $117.3085   $117.31   $117.30   $117.30  
  Purchase #5 $93.92   4.397%   $98.0497   $98.05   $98.05   $98.00  
  Purchase #6 $218.53   3.416%   $225.995   $226.00   $226.00   $226.00  
  Purchase #7 $80.37   5.798%   $85.0299   $85.03   $85.05   $85.00  
  7 purchase totals = $937.91       $991.0667   $991.07   $991.10   $991.00