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	$54.53	5.117%	$57.3203	$57.32	$57.30	$57.30
Purchase #2	$111.75	13.183%	$126.482	$126.48	$126.50	$126.50
Purchase #3	$77.61	10.517%	$85.7722	$85.77	$85.75	$85.80
Purchase #4	$220.33	10.763%	$244.0441	$244.04	$244.05	$244.00
Purchase #5	$94.87	10.713%	$105.0334	$105.03	$105.05	$105.00
Purchase #6	$46.66	8.482%	$50.6177	$50.62	$50.60	$50.60
Purchase #7	$213.95	3.821%	$222.125	$222.13	$222.15	$222.10
7 purchase totals =	$819.70		$891.3947	$891.39	$891.40	$891.30