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	$157.88	6.300%	$167.8264	$167.83	$167.85	$167.80
Purchase #2	$18.30	12.432%	$20.5751	$20.58	$20.60	$20.60
Purchase #3	$16.88	11.103%	$18.7542	$18.75	$18.75	$18.80
Purchase #4	$129.89	7.513%	$139.6486	$139.65	$139.65	$139.60
Purchase #5	$24.63	9.850%	$27.0561	$27.06	$27.05	$27.10
Purchase #6	$152.89	13.730%	$173.8818	$173.88	$173.90	$173.90
Purchase #7	$32.40	3.534%	$33.545	$33.55	$33.55	$33.50
7 purchase totals =	$532.87		$581.2872	$581.30	$581.35	$581.30