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	$103.72	5.786%	$109.7212	$109.72	$109.70	$109.70
Purchase #2	$206.66	11.769%	$230.9818	$230.98	$231.00	$231.00
Purchase #3	$178.50	12.195%	$200.2681	$200.27	$200.25	$200.30
Purchase #4	$45.61	10.854%	$50.5605	$50.56	$50.55	$50.60
Purchase #5	$131.42	11.242%	$146.1942	$146.19	$146.20	$146.20
Purchase #6	$146.46	3.135%	$151.0515	$151.05	$151.05	$151.10
Purchase #7	$176.97	13.458%	$200.7866	$200.79	$200.80	$200.80
7 purchase totals =	$989.34		$1,089.5639	$1,089.56	$1,089.55	$1,089.70