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	$40.45	13.539%	$45.9265	$45.93	$45.95	$45.90
Purchase #2	$52.89	3.202%	$54.5835	$54.58	$54.60	$54.60
Purchase #3	$31.29	8.187%	$33.8517	$33.85	$33.85	$33.90
Purchase #4	$214.80	9.255%	$234.6797	$234.68	$234.70	$234.70
Purchase #5	$15.78	12.434%	$17.7421	$17.74	$17.75	$17.70
Purchase #6	$103.41	6.180%	$109.8007	$109.80	$109.80	$109.80
Purchase #7	$49.72	9.191%	$54.2898	$54.29	$54.30	$54.30
7 purchase totals =	$508.34		$550.8740	$550.87	$550.95	$550.90