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 $53.71   11.129%   $59.6874   $59.69   $59.70   $59.70  
  Purchase #2 $66.30   13.243%   $75.0801   $75.08   $75.10   $75.10  
  Purchase #3 $164.86   12.629%   $185.6802   $185.68   $185.70   $185.70  
  Purchase #4 $192.96   11.106%   $214.3901   $214.39   $214.40   $214.40  
  Purchase #5 $221.63   8.604%   $240.699   $240.70   $240.70   $240.70  
  Purchase #6 $137.44   10.571%   $151.9688   $151.97   $151.95   $152.00  
  Purchase #7 $25.76   9.517%   $28.2116   $28.21   $28.20   $28.20  
  7 purchase totals = $862.66       $955.7172   $955.72   $955.75   $955.80