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	$137.87	13.572%	$156.5817	$156.58	$156.60	$156.60
Purchase #2	$105.99	5.227%	$111.5301	$111.53	$111.55	$111.50
Purchase #3	$130.70	12.194%	$146.6376	$146.64	$146.65	$146.60
Purchase #4	$57.26	9.131%	$62.4884	$62.49	$62.50	$62.50
Purchase #5	$123.53	12.756%	$139.2875	$139.29	$139.30	$139.30
Purchase #6	$66.53	9.380%	$72.7705	$72.77	$72.75	$72.80
Purchase #7	$31.40	13.219%	$35.5508	$35.55	$35.55	$35.60
7 purchase totals =	$653.28		$724.8466	$724.85	$724.90	$724.90