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	$87.37	4.631%	$91.4161	$91.42	$91.40	$91.40
Purchase #2	$243.50	11.495%	$271.4903	$271.49	$271.50	$271.50
Purchase #3	$225.40	8.309%	$244.1285	$244.13	$244.15	$244.10
Purchase #4	$204.28	4.713%	$213.9077	$213.91	$213.90	$213.90
Purchase #5	$142.61	6.629%	$152.0636	$152.06	$152.05	$152.10
Purchase #6	$207.46	10.613%	$229.4777	$229.48	$229.50	$229.50
Purchase #7	$74.28	4.376%	$77.5305	$77.53	$77.55	$77.50
7 purchase totals =	$1,184.90		$1,280.0144	$1,280.02	$1,280.05	$1,280.00