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	$105.47	6.557%	$112.3857	$112.39	$112.40	$112.40
Purchase #2	$158.72	5.521%	$167.4829	$167.48	$167.50	$167.50
Purchase #3	$163.42	6.628%	$174.2515	$174.25	$174.25	$174.30
Purchase #4	$43.52	10.521%	$48.0987	$48.10	$48.10	$48.10
Purchase #5	$52.58	5.790%	$55.6244	$55.62	$55.60	$55.60
Purchase #6	$215.54	4.577%	$225.4053	$225.41	$225.40	$225.40
Purchase #7	$58.66	13.199%	$66.4025	$66.40	$66.40	$66.40
7 purchase totals =	$797.91		$849.6510	$849.65	$849.65	$849.70