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	$25.82	12.567%	$29.0648	$29.06	$29.05	$29.10
Purchase #2	$99.42	11.759%	$111.1108	$111.11	$111.10	$111.10
Purchase #3	$164.52	10.653%	$182.0463	$182.05	$182.05	$182.00
Purchase #4	$9.43	7.552%	$10.1422	$10.14	$10.15	$10.10
Purchase #5	$207.84	9.754%	$228.1127	$228.11	$228.10	$228.10
Purchase #6	$97.92	7.340%	$105.1073	$105.11	$105.10	$105.10
Purchase #7	$228.54	9.591%	$250.4593	$250.46	$250.45	$250.50
7 purchase totals =	$833.49		$916.0434	$916.04	$916.00	$916.00