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	$144.52	9.841%	$158.7422	$158.74	$158.75	$158.70
Purchase #2	$116.73	6.173%	$123.9357	$123.94	$123.95	$123.90
Purchase #3	$152.77	6.592%	$162.8406	$162.84	$162.85	$162.80
Purchase #4	$239.58	7.520%	$257.5964	$257.60	$257.60	$257.60
Purchase #5	$184.39	7.107%	$197.4946	$197.49	$197.50	$197.50
Purchase #6	$74.30	8.284%	$80.455	$80.46	$80.45	$80.50
Purchase #7	$57.27	4.278%	$59.72	$59.72	$59.70	$59.70
7 purchase totals =	$969.56		$1,040.7845	$1,040.79	$1,040.80	$1,040.70