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	$79.65	12.291%	$89.4398	$89.44	$89.45	$89.40
Purchase #2	$59.33	13.456%	$67.3134	$67.31	$67.30	$67.30
Purchase #3	$86.83	3.532%	$89.8968	$89.90	$89.90	$89.90
Purchase #4	$143.41	4.732%	$150.1962	$150.20	$150.20	$150.20
Purchase #5	$107.88	8.421%	$116.9646	$116.96	$116.95	$117.00
Purchase #6	$45.73	12.436%	$51.417	$51.42	$51.40	$51.40
Purchase #7	$160.41	7.857%	$173.0134	$173.01	$173.00	$173.00
7 purchase totals =	$683.24		$738.2412	$738.24	$738.20	$738.20