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	$35.32	13.379%	$40.0455	$40.05	$40.05	$40.00
Purchase #2	$136.35	11.716%	$152.3248	$152.32	$152.30	$152.30
Purchase #3	$133.85	13.152%	$151.454	$151.45	$151.45	$151.50
Purchase #4	$26.65	6.109%	$28.278	$28.28	$28.30	$28.30
Purchase #5	$177.31	7.664%	$190.899	$190.90	$190.90	$190.90
Purchase #6	$82.30	5.163%	$86.5491	$86.55	$86.55	$86.50
Purchase #7	$89.78	5.605%	$94.8122	$94.81	$94.80	$94.80
7 purchase totals =	$681.56		$744.3626	$744.36	$744.35	$744.30