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 $87.44   12.308%   $98.2021   $98.20   $98.20   $98.20  
  Purchase #2 $71.73   6.329%   $76.2698   $76.27   $76.25   $76.30  
  Purchase #3 $48.25   7.114%   $51.6825   $51.68   $51.70   $51.70  
  Purchase #4 $118.76   4.761%   $124.4142   $124.41   $124.40   $124.40  
  Purchase #5 $21.30   7.447%   $22.8862   $22.89   $22.90   $22.90  
  Purchase #6 $86.89   13.626%   $98.7296   $98.73   $98.75   $98.70  
  Purchase #7 $216.39   10.608%   $239.3447   $239.34   $239.35   $239.30  
  7 purchase totals = $650.76       $711.5291   $711.52   $711.55   $711.50