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	$204.42	12.326%	$229.6168	$229.62	$229.60	$229.60
Purchase #2	$166.51	5.802%	$176.1709	$176.17	$176.15	$176.20
Purchase #3	$70.31	11.670%	$78.5152	$78.52	$78.50	$78.50
Purchase #4	$51.39	11.568%	$57.3348	$57.33	$57.35	$57.30
Purchase #5	$74.61	10.492%	$82.4381	$82.44	$82.45	$82.40
Purchase #6	$157.63	13.398%	$178.7493	$178.75	$178.75	$178.70
Purchase #7	$93.30	3.124%	$96.2147	$96.21	$96.20	$96.20
7 purchase totals =	$818.17		$899.0398	$899.04	$899.00	$898.90