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 $116.80   13.472%   $132.5353   $132.54   $132.55   $132.50  
  Purchase #2 $132.80   6.326%   $141.2009   $141.20   $141.20   $141.20  
  Purchase #3 $194.86   10.175%   $214.687   $214.69   $214.70   $214.70  
  Purchase #4 $144.38   6.593%   $153.899   $153.90   $153.90   $153.90  
  Purchase #5 $136.66   9.593%   $149.7698   $149.77   $149.75   $149.80  
  Purchase #6 $117.50   8.457%   $127.437   $127.44   $127.45   $127.40  
  Purchase #7 $54.76   9.584%   $60.0082   $60.01   $60.00   $60.00  
  7 purchase totals = $897.76       $979.5372   $979.55   $979.55   $979.50