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	$154.41	12.302%	$173.4055	$173.41	$173.40	$173.40
Purchase #2	$156.64	8.815%	$170.4478	$170.45	$170.45	$170.40
Purchase #3	$120.51	5.423%	$127.0453	$127.05	$127.05	$127.00
Purchase #4	$152.78	8.720%	$166.1024	$166.10	$166.10	$166.10
Purchase #5	$88.74	12.343%	$99.6932	$99.69	$99.70	$99.70
Purchase #6	$78.26	5.120%	$82.2669	$82.27	$82.25	$82.30
Purchase #7	$74.78	8.540%	$81.1662	$81.17	$81.15	$81.20
7 purchase totals =	$826.12		$900.1273	$900.14	$900.10	$900.10