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	$115.29	7.353%	$123.7673	$123.77	$123.75	$123.80
Purchase #2	$135.64	11.657%	$151.4516	$151.45	$151.45	$151.50
Purchase #3	$95.64	4.370%	$99.8195	$99.82	$99.80	$99.80
Purchase #4	$144.32	5.399%	$152.1118	$152.11	$152.10	$152.10
Purchase #5	$93.86	9.535%	$102.8096	$102.81	$102.80	$102.80
Purchase #6	$47.93	3.463%	$49.5898	$49.59	$49.60	$49.60
Purchase #7	$123.80	6.343%	$131.6526	$131.65	$131.65	$131.70
7 purchase totals =	$756.48		$811.2022	$811.20	$811.15	$811.30