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	$189.76	8.113%	$205.1552	$205.16	$205.15	$205.20
Purchase #2	$229.38	12.258%	$257.4974	$257.50	$257.50	$257.50
Purchase #3	$96.97	7.183%	$103.9354	$103.94	$103.95	$103.90
Purchase #4	$172.41	10.866%	$191.1441	$191.14	$191.15	$191.10
Purchase #5	$105.70	5.779%	$111.8084	$111.81	$111.80	$111.80
Purchase #6	$57.96	5.691%	$61.2585	$61.26	$61.25	$61.30
Purchase #7	$36.76	6.288%	$39.0715	$39.07	$39.05	$39.10
7 purchase totals =	$888.94		$969.8705	$969.88	$969.85	$969.90