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	$173.66	7.336%	$186.3997	$186.40	$186.40	$186.40
Purchase #2	$166.76	13.521%	$189.3076	$189.31	$189.30	$189.30
Purchase #3	$242.84	5.233%	$255.5478	$255.55	$255.55	$255.50
Purchase #4	$153.93	13.792%	$175.16	$175.16	$175.15	$175.20
Purchase #5	$94.29	4.434%	$98.4708	$98.47	$98.45	$98.50
Purchase #6	$240.53	6.659%	$256.5469	$256.55	$256.55	$256.50
Purchase #7	$99.44	9.397%	$108.7844	$108.78	$108.80	$108.80
7 purchase totals =	$1,171.45		$1,270.2172	$1,270.22	$1,270.20	$1,270.20