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	$204.47	9.670%	$224.2422	$224.24	$224.25	$224.20
Purchase #2	$79.44	8.452%	$86.1543	$86.15	$86.15	$86.20
Purchase #3	$10.52	13.487%	$11.9388	$11.94	$11.95	$11.90
Purchase #4	$159.28	4.672%	$166.7216	$166.72	$166.70	$166.70
Purchase #5	$138.40	11.450%	$154.2468	$154.25	$154.25	$154.20
Purchase #6	$165.79	3.826%	$172.1331	$172.13	$172.15	$172.10
Purchase #7	$27.42	4.755%	$28.7238	$28.72	$28.70	$28.70
7 purchase totals =	$785.32		$844.1606	$844.15	$844.15	$844.00