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	$155.92	9.838%	$171.2594	$171.26	$171.25	$171.30
Purchase #2	$92.74	13.160%	$104.9446	$104.94	$104.95	$104.90
Purchase #3	$105.31	5.701%	$111.3137	$111.31	$111.30	$111.30
Purchase #4	$12.88	9.819%	$14.1447	$14.14	$14.15	$14.10
Purchase #5	$62.64	8.607%	$68.0314	$68.03	$68.05	$68.00
Purchase #6	$128.61	9.117%	$140.3354	$140.34	$140.35	$140.30
Purchase #7	$156.78	8.166%	$169.5827	$169.58	$169.60	$169.60
7 purchase totals =	$714.88		$779.6119	$779.60	$779.65	$779.50