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	$87.62	3.762%	$90.9163	$90.92	$90.90	$90.90
Purchase #2	$223.57	4.502%	$233.6351	$233.64	$233.65	$233.60
Purchase #3	$173.52	10.309%	$191.4082	$191.41	$191.40	$191.40
Purchase #4	$15.83	13.844%	$18.0215	$18.02	$18.00	$18.00
Purchase #5	$39.27	9.321%	$42.9304	$42.93	$42.95	$42.90
Purchase #6	$166.84	5.700%	$176.3499	$176.35	$176.35	$176.30
Purchase #7	$219.58	6.476%	$233.8	$233.80	$233.80	$233.80
7 purchase totals =	$926.23		$987.0614	$987.07	$987.05	$986.90