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	$228.86	9.265%	$250.0639	$250.06	$250.05	$250.10
Purchase #2	$235.77	7.433%	$253.2948	$253.29	$253.30	$253.30
Purchase #3	$73.74	8.577%	$80.0647	$80.06	$80.05	$80.10
Purchase #4	$39.32	3.566%	$40.7222	$40.72	$40.70	$40.70
Purchase #5	$166.72	13.618%	$189.4239	$189.42	$189.40	$189.40
Purchase #6	$8.92	13.634%	$10.1362	$10.14	$10.15	$10.10
Purchase #7	$70.76	11.205%	$78.6887	$78.69	$78.70	$78.70
7 purchase totals =	$824.09		$902.3944	$902.38	$902.35	$902.40