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	$165.91	10.671%	$183.6143	$183.61	$183.60	$183.60
Purchase #2	$82.58	10.787%	$91.4879	$91.49	$91.50	$91.50
Purchase #3	$78.77	4.742%	$82.5053	$82.51	$82.50	$82.50
Purchase #4	$196.45	12.414%	$220.8373	$220.84	$220.85	$220.80
Purchase #5	$246.52	3.699%	$255.6388	$255.64	$255.65	$255.60
Purchase #6	$247.52	5.629%	$261.4529	$261.45	$261.45	$261.50
Purchase #7	$125.40	4.261%	$130.7433	$130.74	$130.75	$130.70
7 purchase totals =	$1,143.15		$1,226.2798	$1,226.28	$1,226.30	$1,226.20