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	$165.83	7.258%	$177.8659	$177.87	$177.85	$177.90
Purchase #2	$108.30	6.812%	$115.6774	$115.68	$115.70	$115.70
Purchase #3	$162.62	4.485%	$169.9135	$169.91	$169.90	$169.90
Purchase #4	$46.45	3.613%	$48.1282	$48.13	$48.15	$48.10
Purchase #5	$79.77	13.296%	$90.3762	$90.38	$90.40	$90.40
Purchase #6	$138.42	9.777%	$151.9533	$151.95	$151.95	$152.00
Purchase #7	$41.47	9.715%	$45.4988	$45.50	$45.50	$45.50
7 purchase totals =	$742.86		$799.4133	$799.42	$799.45	$799.50