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	$128.97	6.443%	$137.2795	$137.28	$137.30	$137.30
Purchase #2	$49.29	7.634%	$53.0528	$53.05	$53.05	$53.10
Purchase #3	$75.46	13.619%	$85.7369	$85.74	$85.75	$85.70
Purchase #4	$177.45	7.406%	$190.5919	$190.59	$190.60	$190.60
Purchase #5	$27.37	3.221%	$28.2516	$28.25	$28.25	$28.30
Purchase #6	$233.83	12.336%	$262.6753	$262.68	$262.70	$262.70
Purchase #7	$163.49	12.835%	$184.4739	$184.47	$184.45	$184.50
7 purchase totals =	$855.86		$942.0619	$942.06	$942.10	$942.20