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 $104.91   9.422%   $114.7946   $114.79   $114.80   $114.80  
  Purchase #2 $70.49   8.830%   $76.7143   $76.71   $76.70   $76.70  
  Purchase #3 $136.42   10.817%   $151.1766   $151.18   $151.20   $151.20  
  Purchase #4 $98.52   5.269%   $103.711   $103.71   $103.70   $103.70  
  Purchase #5 $65.44   10.829%   $72.5265   $72.53   $72.55   $72.50  
  Purchase #6 $231.25   3.641%   $239.6698   $239.67   $239.65   $239.70  
  Purchase #7 $96.74   8.286%   $104.7559   $104.76   $104.75   $104.80  
  7 purchase totals = $803.77       $863.3487   $863.35   $863.35   $863.40