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	$80.56	12.721%	$90.808	$90.81	$90.80	$90.80
Purchase #2	$177.91	4.383%	$185.7078	$185.71	$185.70	$185.70
Purchase #3	$136.82	6.805%	$146.1306	$146.13	$146.15	$146.10
Purchase #4	$95.27	10.557%	$105.3277	$105.33	$105.35	$105.30
Purchase #5	$140.99	5.185%	$148.3003	$148.30	$148.30	$148.30
Purchase #6	$198.99	3.426%	$205.8074	$205.81	$205.80	$205.80
Purchase #7	$226.50	3.528%	$234.4909	$234.49	$234.50	$234.50
7 purchase totals =	$1,057.04		$1,116.5727	$1,116.58	$1,116.60	$1,116.50