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	$40.30	8.165%	$43.5905	$43.59	$43.60	$43.60
Purchase #2	$143.30	9.844%	$157.4065	$157.41	$157.40	$157.40
Purchase #3	$146.92	10.525%	$162.3833	$162.38	$162.40	$162.40
Purchase #4	$214.49	7.121%	$229.7638	$229.76	$229.75	$229.80
Purchase #5	$70.95	10.690%	$78.5346	$78.53	$78.55	$78.50
Purchase #6	$43.54	13.203%	$49.2886	$49.29	$49.30	$49.30
Purchase #7	$200.31	7.685%	$215.7038	$215.70	$215.70	$215.70
7 purchase totals =	$859.81		$936.6711	$936.66	$936.70	$936.70