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	$101.77	10.632%	$112.5902	$112.59	$112.60	$112.60
Purchase #2	$77.92	6.777%	$83.2006	$83.20	$83.20	$83.20
Purchase #3	$217.61	11.600%	$242.8528	$242.85	$242.85	$242.90
Purchase #4	$247.35	7.301%	$265.409	$265.41	$265.40	$265.40
Purchase #5	$51.87	7.680%	$55.8536	$55.85	$55.85	$55.90
Purchase #6	$87.86	12.319%	$98.6835	$98.68	$98.70	$98.70
Purchase #7	$48.86	3.370%	$50.5066	$50.51	$50.50	$50.50
7 purchase totals =	$833.24		$909.0963	$909.09	$909.10	$909.20