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	$231.94	4.396%	$242.1361	$242.14	$242.15	$242.10
Purchase #2	$105.94	13.547%	$120.2917	$120.29	$120.30	$120.30
Purchase #3	$151.75	9.838%	$166.6792	$166.68	$166.70	$166.70
Purchase #4	$51.83	6.531%	$55.215	$55.22	$55.20	$55.20
Purchase #5	$66.98	6.476%	$71.3176	$71.32	$71.30	$71.30
Purchase #6	$42.62	13.562%	$48.4001	$48.40	$48.40	$48.40
Purchase #7	$50.86	5.833%	$53.8267	$53.83	$53.85	$53.80
7 purchase totals =	$701.92		$757.8664	$757.88	$757.90	$757.80