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	$101.35	9.820%	$111.3026	$111.30	$111.30	$111.30
Purchase #2	$125.74	3.141%	$129.6895	$129.69	$129.70	$129.70
Purchase #3	$202.63	3.388%	$209.4951	$209.50	$209.50	$209.50
Purchase #4	$105.60	5.284%	$111.1799	$111.18	$111.20	$111.20
Purchase #5	$192.79	3.225%	$199.0075	$199.01	$199.00	$199.00
Purchase #6	$39.59	12.252%	$44.4406	$44.44	$44.45	$44.40
Purchase #7	$36.38	13.445%	$41.2713	$41.27	$41.25	$41.30
7 purchase totals =	$804.08		$846.3865	$846.39	$846.40	$846.40