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	$123.67	4.522%	$129.2624	$129.26	$129.25	$129.30
Purchase #2	$198.31	5.731%	$209.6751	$209.68	$209.70	$209.70
Purchase #3	$244.89	5.598%	$258.5989	$258.60	$258.60	$258.60
Purchase #4	$82.92	9.608%	$90.887	$90.89	$90.90	$90.90
Purchase #5	$81.47	12.320%	$91.5071	$91.51	$91.50	$91.50
Purchase #6	$146.41	5.583%	$154.5841	$154.58	$154.60	$154.60
Purchase #7	$161.85	11.470%	$180.4142	$180.41	$180.40	$180.40
7 purchase totals =	$1,039.52		$1,114.9288	$1,114.93	$1,114.95	$1,115.00