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	$227.80	6.563%	$242.7505	$242.75	$242.75	$242.80
Purchase #2	$77.25	4.446%	$80.6845	$80.68	$80.70	$80.70
Purchase #3	$83.28	9.518%	$91.2066	$91.21	$91.20	$91.20
Purchase #4	$10.25	7.108%	$10.9786	$10.98	$11.00	$11.00
Purchase #5	$146.98	12.384%	$165.182	$165.18	$165.20	$165.20
Purchase #6	$59.79	12.831%	$67.4617	$67.46	$67.45	$67.50
Purchase #7	$126.69	12.190%	$142.1335	$142.13	$142.15	$142.10
7 purchase totals =	$732.04		$800.3974	$800.39	$800.45	$800.50