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	$151.52	3.858%	$157.3656	$157.37	$157.35	$157.40
Purchase #2	$144.90	9.576%	$158.7756	$158.78	$158.80	$158.80
Purchase #3	$237.83	6.874%	$254.1784	$254.18	$254.20	$254.20
Purchase #4	$247.54	6.707%	$264.1425	$264.14	$264.15	$264.10
Purchase #5	$74.81	9.635%	$82.0179	$82.02	$82.00	$82.00
Purchase #6	$55.87	9.328%	$61.0816	$61.08	$61.10	$61.10
Purchase #7	$107.31	4.345%	$111.9726	$111.97	$111.95	$112.00
7 purchase totals =	$1,019.78		$1,089.5342	$1,089.54	$1,089.55	$1,089.60