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	$216.70	11.716%	$242.0886	$242.09	$242.10	$242.10
Purchase #2	$205.61	9.374%	$224.8839	$224.88	$224.90	$224.90
Purchase #3	$161.41	7.513%	$173.5367	$173.54	$173.55	$173.50
Purchase #4	$92.31	7.424%	$99.1631	$99.16	$99.15	$99.20
Purchase #5	$94.29	7.866%	$101.7069	$101.71	$101.70	$101.70
Purchase #6	$30.29	10.365%	$33.4296	$33.43	$33.45	$33.40
Purchase #7	$135.68	6.697%	$144.7665	$144.77	$144.75	$144.80
7 purchase totals =	$936.29		$1,019.5753	$1,019.58	$1,019.60	$1,019.60