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 $8.94   10.407%   $9.8704   $9.87   $9.85   $9.90  
  Purchase #2 $70.30   9.579%   $77.034   $77.03   $77.05   $77.00  
  Purchase #3 $42.78   9.787%   $46.9669   $46.97   $46.95   $47.00  
  Purchase #4 $21.76   3.139%   $22.443   $22.44   $22.45   $22.40  
  Purchase #5 $150.38   4.713%   $157.4674   $157.47   $157.45   $157.50  
  Purchase #6 $51.43   6.494%   $54.7699   $54.77   $54.75   $54.80  
  Purchase #7 $204.49   5.540%   $215.8187   $215.82   $215.80   $215.80  
  7 purchase totals = $550.08       $584.3703   $584.37   $584.30   $584.40