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	$60.88	9.666%	$66.7647	$66.76	$66.75	$66.80
Purchase #2	$117.52	10.713%	$130.1099	$130.11	$130.10	$130.10
Purchase #3	$230.30	7.478%	$247.5218	$247.52	$247.50	$247.50
Purchase #4	$46.85	5.824%	$49.5785	$49.58	$49.60	$49.60
Purchase #5	$104.93	6.574%	$111.8281	$111.83	$111.85	$111.80
Purchase #6	$207.69	7.835%	$223.9625	$223.96	$223.95	$224.00
Purchase #7	$84.65	5.339%	$89.1695	$89.17	$89.15	$89.20
7 purchase totals =	$852.82		$918.9350	$918.93	$918.90	$919.00