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	$59.62	8.151%	$64.4796	$64.48	$64.50	$64.50
Purchase #2	$129.72	13.147%	$146.7743	$146.77	$146.75	$146.80
Purchase #3	$244.36	3.146%	$252.0476	$252.05	$252.05	$252.00
Purchase #4	$164.27	10.158%	$180.9565	$180.96	$180.95	$181.00
Purchase #5	$102.41	11.780%	$114.4739	$114.47	$114.45	$114.50
Purchase #6	$54.82	12.826%	$61.8512	$61.85	$61.85	$61.90
Purchase #7	$54.61	3.620%	$56.5869	$56.59	$56.60	$56.60
7 purchase totals =	$809.81		$877.1700	$877.17	$877.15	$877.30