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	$93.52	13.269%	$105.9292	$105.93	$105.95	$105.90
Purchase #2	$250.65	6.848%	$267.8145	$267.81	$267.80	$267.80
Purchase #3	$80.85	10.722%	$89.5187	$89.52	$89.50	$89.50
Purchase #4	$42.52	3.240%	$43.8976	$43.90	$43.90	$43.90
Purchase #5	$134.27	9.464%	$146.9773	$146.98	$147.00	$147.00
Purchase #6	$38.51	12.825%	$43.4489	$43.45	$43.45	$43.40
Purchase #7	$147.85	5.225%	$155.5752	$155.58	$155.60	$155.60
7 purchase totals =	$788.17		$853.1614	$853.17	$853.20	$853.10