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	$183.51	8.136%	$198.4404	$198.44	$198.45	$198.40
Purchase #2	$79.80	12.327%	$89.6369	$89.64	$89.65	$89.60
Purchase #3	$132.66	4.141%	$138.1535	$138.15	$138.15	$138.20
Purchase #4	$51.68	9.700%	$56.693	$56.69	$56.70	$56.70
Purchase #5	$81.55	7.658%	$87.7951	$87.80	$87.80	$87.80
Purchase #6	$115.60	10.434%	$127.6617	$127.66	$127.65	$127.70
Purchase #7	$79.43	12.824%	$89.6161	$89.62	$89.60	$89.60
7 purchase totals =	$724.23		$787.9967	$788.00	$788.00	$788.00