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	$37.43	9.147%	$40.8537	$40.85	$40.85	$40.90
Purchase #2	$95.72	7.831%	$103.2158	$103.22	$103.20	$103.20
Purchase #3	$149.73	6.647%	$159.6826	$159.68	$159.70	$159.70
Purchase #4	$223.41	6.204%	$237.2704	$237.27	$237.25	$237.30
Purchase #5	$151.78	6.805%	$162.1086	$162.11	$162.10	$162.10
Purchase #6	$247.78	9.556%	$271.4579	$271.46	$271.45	$271.50
Purchase #7	$190.38	4.592%	$199.1222	$199.12	$199.10	$199.10
7 purchase totals =	$1,096.23		$1,173.7112	$1,173.71	$1,173.65	$1,173.80