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	$45.67	10.620%	$50.5202	$50.52	$50.50	$50.50
Purchase #2	$142.85	5.681%	$150.9653	$150.97	$150.95	$151.00
Purchase #3	$11.50	5.667%	$12.1517	$12.15	$12.15	$12.20
Purchase #4	$50.70	4.872%	$53.1701	$53.17	$53.15	$53.20
Purchase #5	$227.59	12.156%	$255.2558	$255.26	$255.25	$255.30
Purchase #6	$83.68	12.429%	$94.0806	$94.08	$94.10	$94.10
Purchase #7	$193.44	11.782%	$216.2311	$216.23	$216.25	$216.20
7 purchase totals =	$755.43		$832.3748	$832.38	$832.35	$832.50