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	$233.77	3.564%	$242.1016	$242.10	$242.10	$242.10
Purchase #2	$177.56	8.185%	$192.0933	$192.09	$192.10	$192.10
Purchase #3	$45.89	6.153%	$48.7136	$48.71	$48.70	$48.70
Purchase #4	$181.81	7.336%	$195.1476	$195.15	$195.15	$195.10
Purchase #5	$170.45	6.437%	$181.4219	$181.42	$181.40	$181.40
Purchase #6	$99.61	11.715%	$111.2793	$111.28	$111.30	$111.30
Purchase #7	$10.64	13.828%	$12.1113	$12.11	$12.10	$12.10
7 purchase totals =	$919.73		$982.8686	$982.86	$982.85	$982.80