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	$144.47	12.402%	$162.3872	$162.39	$162.40	$162.40
Purchase #2	$48.29	8.486%	$52.3879	$52.39	$52.40	$52.40
Purchase #3	$107.56	3.665%	$111.5021	$111.50	$111.50	$111.50
Purchase #4	$40.52	7.773%	$43.6696	$43.67	$43.65	$43.70
Purchase #5	$238.85	9.574%	$261.7175	$261.72	$261.70	$261.70
Purchase #6	$29.95	12.683%	$33.7486	$33.75	$33.75	$33.70
Purchase #7	$227.96	8.658%	$247.6968	$247.70	$247.70	$247.70
7 purchase totals =	$837.60		$913.1097	$913.12	$913.10	$913.10