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	$99.42	12.337%	$111.6854	$111.69	$111.70	$111.70
Purchase #2	$130.70	13.139%	$147.8727	$147.87	$147.85	$147.90
Purchase #3	$90.45	10.545%	$99.988	$99.99	$100.00	$100.00
Purchase #4	$230.78	9.688%	$253.138	$253.14	$253.15	$253.10
Purchase #5	$94.76	13.779%	$107.817	$107.82	$107.80	$107.80
Purchase #6	$44.40	11.409%	$49.4656	$49.47	$49.45	$49.50
Purchase #7	$206.37	8.708%	$224.3407	$224.34	$224.35	$224.30
7 purchase totals =	$896.88		$994.3074	$994.32	$994.30	$994.30