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	$88.74	12.149%	$99.521	$99.52	$99.50	$99.50
Purchase #2	$97.45	10.650%	$107.8284	$107.83	$107.85	$107.80
Purchase #3	$11.73	7.480%	$12.6074	$12.61	$12.60	$12.60
Purchase #4	$82.40	9.735%	$90.4216	$90.42	$90.40	$90.40
Purchase #5	$115.79	10.294%	$127.7094	$127.71	$127.70	$127.70
Purchase #6	$45.49	4.624%	$47.5935	$47.59	$47.60	$47.60
Purchase #7	$205.52	4.111%	$213.9689	$213.97	$213.95	$214.00
7 purchase totals =	$647.12		$699.6502	$699.65	$699.60	$699.60