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	$81.47	12.176%	$91.3898	$91.39	$91.40	$91.40
Purchase #2	$248.28	4.126%	$258.524	$258.52	$258.50	$258.50
Purchase #3	$237.26	7.732%	$255.6049	$255.60	$255.60	$255.60
Purchase #4	$174.55	13.612%	$198.3097	$198.31	$198.30	$198.30
Purchase #5	$21.53	7.616%	$23.1697	$23.17	$23.15	$23.20
Purchase #6	$139.38	3.866%	$144.7684	$144.77	$144.75	$144.80
Purchase #7	$38.63	4.722%	$40.4541	$40.45	$40.45	$40.50
7 purchase totals =	$941.10		$1,012.2206	$1,012.21	$1,012.15	$1,012.30