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	$40.31	4.662%	$42.1893	$42.19	$42.20	$42.20
Purchase #2	$159.88	10.652%	$176.9104	$176.91	$176.90	$176.90
Purchase #3	$39.40	4.386%	$41.1281	$41.13	$41.15	$41.10
Purchase #4	$99.69	11.395%	$111.0497	$111.05	$111.05	$111.00
Purchase #5	$172.39	12.867%	$194.5714	$194.57	$194.55	$194.60
Purchase #6	$44.40	5.723%	$46.941	$46.94	$46.95	$46.90
Purchase #7	$106.31	4.703%	$111.3098	$111.31	$111.30	$111.30
7 purchase totals =	$662.38		$724.0997	$724.10	$724.10	$724.00