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	$72.93	5.323%	$76.8121	$76.81	$76.80	$76.80
Purchase #2	$29.39	10.194%	$32.386	$32.39	$32.40	$32.40
Purchase #3	$73.63	12.117%	$82.5517	$82.55	$82.55	$82.60
Purchase #4	$192.26	6.806%	$205.3452	$205.35	$205.35	$205.30
Purchase #5	$124.68	4.874%	$130.7569	$130.76	$130.75	$130.80
Purchase #6	$98.56	11.244%	$109.6421	$109.64	$109.65	$109.60
Purchase #7	$79.26	5.763%	$83.8278	$83.83	$83.85	$83.80
7 purchase totals =	$670.71		$721.3218	$721.33	$721.35	$721.30