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	$65.91	9.531%	$72.1919	$72.19	$72.20	$72.20
Purchase #2	$202.38	13.594%	$229.8915	$229.89	$229.90	$229.90
Purchase #3	$103.43	7.532%	$111.2203	$111.22	$111.20	$111.20
Purchase #4	$139.46	6.857%	$149.0228	$149.02	$149.00	$149.00
Purchase #5	$86.99	3.398%	$89.9459	$89.95	$89.95	$89.90
Purchase #6	$145.25	11.161%	$161.4614	$161.46	$161.45	$161.50
Purchase #7	$126.48	5.255%	$133.1265	$133.13	$133.15	$133.10
7 purchase totals =	$869.90		$946.8603	$946.86	$946.85	$946.80