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	$67.48	6.413%	$71.8075	$71.81	$71.80	$71.80
Purchase #2	$147.99	3.666%	$153.4153	$153.42	$153.40	$153.40
Purchase #3	$107.45	10.817%	$119.0729	$119.07	$119.05	$119.10
Purchase #4	$54.42	5.163%	$57.2297	$57.23	$57.25	$57.20
Purchase #5	$111.44	13.402%	$126.3752	$126.38	$126.40	$126.40
Purchase #6	$33.50	11.358%	$37.3049	$37.30	$37.30	$37.30
Purchase #7	$115.99	6.558%	$123.5966	$123.60	$123.60	$123.60
7 purchase totals =	$638.27		$688.8021	$688.81	$688.80	$688.80