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	$36.69	9.342%	$40.1176	$40.12	$40.10	$40.10
Purchase #2	$131.30	9.478%	$143.7446	$143.74	$143.75	$143.70
Purchase #3	$97.51	13.835%	$111.0005	$111.00	$111.00	$111.00
Purchase #4	$135.56	7.411%	$145.6064	$145.61	$145.60	$145.60
Purchase #5	$90.82	3.722%	$94.2003	$94.20	$94.20	$94.20
Purchase #6	$84.58	6.494%	$90.0726	$90.07	$90.05	$90.10
Purchase #7	$230.92	4.285%	$240.8149	$240.81	$240.80	$240.80
7 purchase totals =	$807.38		$865.5569	$865.55	$865.50	$865.50