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	$40.75	7.416%	$43.772	$43.77	$43.75	$43.80
Purchase #2	$122.89	3.298%	$126.9429	$126.94	$126.95	$126.90
Purchase #3	$82.82	9.835%	$90.9653	$90.97	$90.95	$91.00
Purchase #4	$44.33	4.643%	$46.3882	$46.39	$46.40	$46.40
Purchase #5	$186.42	10.480%	$205.9568	$205.96	$205.95	$206.00
Purchase #6	$54.37	12.271%	$61.0417	$61.04	$61.05	$61.00
Purchase #7	$52.32	13.188%	$59.22	$59.22	$59.20	$59.20
7 purchase totals =	$583.90		$634.2869	$634.29	$634.25	$634.30