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	$231.56	11.577%	$258.3677	$258.37	$258.35	$258.40
Purchase #2	$107.46	12.348%	$120.7292	$120.73	$120.75	$120.70
Purchase #3	$215.31	10.822%	$238.6108	$238.61	$238.60	$238.60
Purchase #4	$144.83	11.479%	$161.455	$161.46	$161.45	$161.50
Purchase #5	$233.54	7.119%	$250.1657	$250.17	$250.15	$250.20
Purchase #6	$112.64	13.636%	$127.9996	$128.00	$128.00	$128.00
Purchase #7	$34.38	11.332%	$38.2759	$38.28	$38.30	$38.30
7 purchase totals =	$1,079.72		$1,195.6039	$1,195.62	$1,195.60	$1,195.70