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	$228.49	11.788%	$255.4244	$255.42	$255.40	$255.40
Purchase #2	$157.80	8.768%	$171.6359	$171.64	$171.65	$171.60
Purchase #3	$37.77	11.643%	$42.1676	$42.17	$42.15	$42.20
Purchase #4	$163.40	12.761%	$184.2515	$184.25	$184.25	$184.30
Purchase #5	$143.98	4.604%	$150.6088	$150.61	$150.60	$150.60
Purchase #6	$108.81	5.869%	$115.1961	$115.20	$115.20	$115.20
Purchase #7	$36.40	12.182%	$40.8342	$40.83	$40.85	$40.80
7 purchase totals =	$876.65		$960.1185	$960.12	$960.10	$960.10