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 $205.45   9.819%   $225.6231   $225.62   $225.60   $225.60  
  Purchase #2 $148.76   5.872%   $157.4952   $157.50   $157.50   $157.50  
  Purchase #3 $212.54   8.769%   $231.1776   $231.18   $231.20   $231.20  
  Purchase #4 $244.51   9.688%   $268.1981   $268.20   $268.20   $268.20  
  Purchase #5 $58.66   5.233%   $61.7297   $61.73   $61.75   $61.70  
  Purchase #6 $21.73   4.769%   $22.7663   $22.77   $22.75   $22.80  
  Purchase #7 $53.87   6.284%   $57.2552   $57.26   $57.25   $57.30  
  7 purchase totals = $945.52       $1,024.2452   $1,024.26   $1,024.25   $1,024.30