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	$129.50	13.309%	$146.7352	$146.74	$146.75	$146.70
Purchase #2	$78.67	4.500%	$82.2102	$82.21	$82.20	$82.20
Purchase #3	$98.83	13.439%	$112.1118	$112.11	$112.10	$112.10
Purchase #4	$158.43	11.459%	$176.5845	$176.58	$176.60	$176.60
Purchase #5	$184.72	11.314%	$205.6192	$205.62	$205.60	$205.60
Purchase #6	$194.95	11.526%	$217.4199	$217.42	$217.40	$217.40
Purchase #7	$60.70	3.454%	$62.7966	$62.80	$62.80	$62.80
7 purchase totals =	$905.80		$1,003.4774	$1,003.48	$1,003.45	$1,003.40