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	$58.86	11.205%	$65.4553	$65.46	$65.45	$65.50
Purchase #2	$172.32	4.347%	$179.8108	$179.81	$179.80	$179.80
Purchase #3	$101.94	6.461%	$108.5263	$108.53	$108.55	$108.50
Purchase #4	$144.59	13.599%	$164.2528	$164.25	$164.25	$164.30
Purchase #5	$130.50	5.444%	$137.6044	$137.60	$137.60	$137.60
Purchase #6	$101.63	13.551%	$115.4019	$115.40	$115.40	$115.40
Purchase #7	$115.47	13.123%	$130.6231	$130.62	$130.60	$130.60
7 purchase totals =	$825.31		$901.6746	$901.67	$901.65	$901.70