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	$64.45	6.582%	$68.6921	$68.69	$68.70	$68.70
Purchase #2	$227.83	5.654%	$240.7115	$240.71	$240.70	$240.70
Purchase #3	$117.83	4.427%	$123.0463	$123.05	$123.05	$123.00
Purchase #4	$16.44	11.250%	$18.2895	$18.29	$18.30	$18.30
Purchase #5	$157.89	9.116%	$172.2833	$172.28	$172.30	$172.30
Purchase #6	$68.90	10.333%	$76.0194	$76.02	$76.00	$76.00
Purchase #7	$37.43	13.647%	$42.5381	$42.54	$42.55	$42.50
7 purchase totals =	$690.77		$741.5802	$741.58	$741.60	$741.50