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	$172.83	13.458%	$196.0895	$196.09	$196.10	$196.10
Purchase #2	$78.52	13.397%	$89.0393	$89.04	$89.05	$89.00
Purchase #3	$141.99	11.607%	$158.4708	$158.47	$158.45	$158.50
Purchase #4	$215.50	11.601%	$240.5002	$240.50	$240.50	$240.50
Purchase #5	$173.56	4.451%	$181.2852	$181.29	$181.30	$181.30
Purchase #6	$84.39	8.599%	$91.6467	$91.65	$91.65	$91.60
Purchase #7	$242.66	6.665%	$258.8333	$258.83	$258.85	$258.80
7 purchase totals =	$1,109.45		$1,215.8650	$1,215.87	$1,215.90	$1,215.80