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	$138.43	10.709%	$153.2545	$153.25	$153.25	$153.30
Purchase #2	$249.55	9.332%	$272.838	$272.84	$272.85	$272.80
Purchase #3	$172.64	6.541%	$183.9324	$183.93	$183.95	$183.90
Purchase #4	$240.96	3.693%	$249.8587	$249.86	$249.85	$249.90
Purchase #5	$148.60	6.531%	$158.3051	$158.31	$158.30	$158.30
Purchase #6	$104.32	7.255%	$111.8884	$111.89	$111.90	$111.90
Purchase #7	$155.33	12.452%	$174.6717	$174.67	$174.65	$174.70
7 purchase totals =	$1,209.83		$1,304.7488	$1,304.75	$1,304.75	$1,304.80