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	$93.32	6.720%	$99.5911	$99.59	$99.60	$99.60
Purchase #2	$118.44	4.274%	$123.5021	$123.50	$123.50	$123.50
Purchase #3	$94.60	7.442%	$101.6401	$101.64	$101.65	$101.60
Purchase #4	$88.59	11.592%	$98.8594	$98.86	$98.85	$98.90
Purchase #5	$5.51	9.867%	$6.0537	$6.05	$6.05	$6.10
Purchase #6	$61.86	7.631%	$66.5805	$66.58	$66.60	$66.60
Purchase #7	$55.87	3.103%	$57.6036	$57.60	$57.60	$57.60
7 purchase totals =	$518.19		$553.8305	$553.82	$553.85	$553.90