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	$207.38	11.290%	$230.7932	$230.79	$230.80	$230.80
Purchase #2	$50.87	11.640%	$56.7913	$56.79	$56.80	$56.80
Purchase #3	$82.80	6.560%	$88.2317	$88.23	$88.25	$88.20
Purchase #4	$158.47	4.292%	$165.2715	$165.27	$165.25	$165.30
Purchase #5	$193.98	8.859%	$211.1647	$211.16	$211.15	$211.20
Purchase #6	$48.82	5.513%	$51.5114	$51.51	$51.50	$51.50
Purchase #7	$28.32	12.472%	$31.8521	$31.85	$31.85	$31.90
7 purchase totals =	$770.64		$835.6159	$835.60	$835.60	$835.70