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	$130.93	10.433%	$144.5899	$144.59	$144.60	$144.60
Purchase #2	$139.61	13.400%	$158.3177	$158.32	$158.30	$158.30
Purchase #3	$183.42	5.506%	$193.5191	$193.52	$193.50	$193.50
Purchase #4	$207.92	11.537%	$231.9077	$231.91	$231.90	$231.90
Purchase #5	$138.70	5.647%	$146.5324	$146.53	$146.55	$146.50
Purchase #6	$139.54	12.195%	$156.5569	$156.56	$156.55	$156.60
Purchase #7	$166.64	11.685%	$186.1119	$186.11	$186.10	$186.10
7 purchase totals =	$1,106.76		$1,217.5356	$1,217.54	$1,217.50	$1,217.50