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 $60.67   3.469%   $62.7746   $62.77   $62.75   $62.80  
  Purchase #2 $213.37   7.553%   $229.4858   $229.49   $229.50   $229.50  
  Purchase #3 $240.64   11.725%   $268.855   $268.86   $268.85   $268.90  
  Purchase #4 $8.39   10.615%   $9.2806   $9.28   $9.30   $9.30  
  Purchase #5 $159.71   11.390%   $177.901   $177.90   $177.90   $177.90  
  Purchase #6 $162.44   13.169%   $183.8317   $183.83   $183.85   $183.80  
  Purchase #7 $59.30   3.318%   $61.2676   $61.27   $61.25   $61.30  
  7 purchase totals = $904.52       $993.3963   $993.40   $993.40   $993.50