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	$248.86	13.227%	$281.7767	$281.78	$281.80	$281.80
Purchase #2	$136.43	10.439%	$150.6719	$150.67	$150.65	$150.70
Purchase #3	$129.33	13.287%	$146.5141	$146.51	$146.50	$146.50
Purchase #4	$158.29	12.117%	$177.47	$177.47	$177.45	$177.50
Purchase #5	$218.56	10.497%	$241.5022	$241.50	$241.50	$241.50
Purchase #6	$57.84	4.795%	$60.6134	$60.61	$60.60	$60.60
Purchase #7	$84.27	10.235%	$92.895	$92.90	$92.90	$92.90
7 purchase totals =	$1,033.58		$1,151.4433	$1,151.44	$1,151.40	$1,151.50