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	$136.90	13.566%	$155.4719	$155.47	$155.45	$155.50
Purchase #2	$102.74	11.795%	$114.8582	$114.86	$114.85	$114.90
Purchase #3	$97.87	13.874%	$111.4485	$111.45	$111.45	$111.40
Purchase #4	$40.97	11.148%	$45.5373	$45.54	$45.55	$45.50
Purchase #5	$158.42	9.303%	$173.1578	$173.16	$173.15	$173.20
Purchase #6	$248.25	6.178%	$263.5869	$263.59	$263.60	$263.60
Purchase #7	$216.97	9.374%	$237.3088	$237.31	$237.30	$237.30
7 purchase totals =	$1,002.12		$1,101.3694	$1,101.38	$1,101.35	$1,101.40