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	$23.33	3.181%	$24.0721	$24.07	$24.05	$24.10
Purchase #2	$164.56	12.680%	$185.4262	$185.43	$185.45	$185.40
Purchase #3	$65.55	6.496%	$69.8081	$69.81	$69.80	$69.80
Purchase #4	$33.83	5.213%	$35.5936	$35.59	$35.60	$35.60
Purchase #5	$44.86	9.452%	$49.1002	$49.10	$49.10	$49.10
Purchase #6	$37.39	10.682%	$41.384	$41.38	$41.40	$41.40
Purchase #7	$134.91	7.418%	$144.9176	$144.92	$144.90	$144.90
7 purchase totals =	$504.43		$550.3018	$550.30	$550.30	$550.30