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	$162.86	12.597%	$183.3755	$183.38	$183.40	$183.40
Purchase #2	$132.80	11.315%	$147.8263	$147.83	$147.85	$147.80
Purchase #3	$29.78	6.819%	$31.8107	$31.81	$31.80	$31.80
Purchase #4	$48.27	4.658%	$50.5184	$50.52	$50.50	$50.50
Purchase #5	$103.81	11.605%	$115.8572	$115.86	$115.85	$115.90
Purchase #6	$105.38	10.141%	$116.0666	$116.07	$116.05	$116.10
Purchase #7	$109.25	13.624%	$124.1342	$124.13	$124.15	$124.10
7 purchase totals =	$692.15		$769.5889	$769.60	$769.60	$769.60