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	$54.79	9.325%	$59.8992	$59.90	$59.90	$59.90
Purchase #2	$222.39	3.185%	$229.4731	$229.47	$229.45	$229.50
Purchase #3	$108.95	9.151%	$118.92	$118.92	$118.90	$118.90
Purchase #4	$8.90	3.701%	$9.2294	$9.23	$9.25	$9.20
Purchase #5	$133.71	12.506%	$150.4318	$150.43	$150.45	$150.40
Purchase #6	$62.82	11.657%	$70.1429	$70.14	$70.15	$70.10
Purchase #7	$13.64	12.139%	$15.2958	$15.30	$15.30	$15.30
7 purchase totals =	$605.20		$653.3922	$653.39	$653.40	$653.30