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	$142.46	5.862%	$150.811	$150.81	$150.80	$150.80
Purchase #2	$128.28	9.439%	$140.3883	$140.39	$140.40	$140.40
Purchase #3	$233.71	9.267%	$255.3679	$255.37	$255.35	$255.40
Purchase #4	$148.64	3.809%	$154.3017	$154.30	$154.30	$154.30
Purchase #5	$69.68	6.419%	$74.1528	$74.15	$74.15	$74.20
Purchase #6	$151.57	9.104%	$165.3689	$165.37	$165.35	$165.40
Purchase #7	$87.32	13.412%	$99.0314	$99.03	$99.05	$99.00
7 purchase totals =	$961.66		$1,039.4220	$1,039.42	$1,039.40	$1,039.50