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	$76.88	6.783%	$82.0948	$82.09	$82.10	$82.10
Purchase #2	$173.85	3.316%	$179.6149	$179.61	$179.60	$179.60
Purchase #3	$39.55	10.659%	$43.7656	$43.77	$43.75	$43.80
Purchase #4	$164.73	4.766%	$172.581	$172.58	$172.60	$172.60
Purchase #5	$70.56	6.573%	$75.1979	$75.20	$75.20	$75.20
Purchase #6	$107.56	5.490%	$113.465	$113.47	$113.45	$113.50
Purchase #7	$21.31	6.515%	$22.6983	$22.70	$22.70	$22.70
7 purchase totals =	$654.44		$689.4175	$689.42	$689.40	$689.50