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	$122.31	13.731%	$139.1044	$139.10	$139.10	$139.10
Purchase #2	$50.42	9.526%	$55.223	$55.22	$55.20	$55.20
Purchase #3	$63.58	10.831%	$70.4663	$70.47	$70.45	$70.50
Purchase #4	$247.58	5.833%	$262.0213	$262.02	$262.00	$262.00
Purchase #5	$227.40	11.394%	$253.31	$253.31	$253.30	$253.30
Purchase #6	$123.38	7.506%	$132.6409	$132.64	$132.65	$132.60
Purchase #7	$157.84	10.178%	$173.905	$173.91	$173.90	$173.90
7 purchase totals =	$992.51		$1,086.6709	$1,086.67	$1,086.60	$1,086.60