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	$11.76	4.734%	$12.3167	$12.32	$12.30	$12.30
Purchase #2	$36.95	8.721%	$40.1724	$40.17	$40.15	$40.20
Purchase #3	$155.59	12.157%	$174.5051	$174.51	$174.50	$174.50
Purchase #4	$173.72	9.388%	$190.0288	$190.03	$190.05	$190.00
Purchase #5	$229.57	9.260%	$250.8282	$250.83	$250.85	$250.80
Purchase #6	$20.68	5.595%	$21.837	$21.84	$21.85	$21.80
Purchase #7	$15.83	12.410%	$17.7945	$17.79	$17.80	$17.80
7 purchase totals =	$644.10		$707.4827	$707.49	$707.50	$707.40