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	$173.57	6.734%	$185.2582	$185.26	$185.25	$185.30
Purchase #2	$237.86	12.529%	$267.6615	$267.66	$267.65	$267.70
Purchase #3	$59.78	10.364%	$65.9756	$65.98	$66.00	$66.00
Purchase #4	$123.51	3.385%	$127.6908	$127.69	$127.70	$127.70
Purchase #5	$70.62	10.608%	$78.1114	$78.11	$78.10	$78.10
Purchase #6	$97.81	8.190%	$105.8206	$105.82	$105.80	$105.80
Purchase #7	$144.62	9.639%	$158.5599	$158.56	$158.55	$158.60
7 purchase totals =	$907.77		$989.0780	$989.08	$989.05	$989.20