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	$123.71	11.548%	$137.996	$138.00	$138.00	$138.00
Purchase #2	$42.50	7.664%	$45.7572	$45.76	$45.75	$45.80
Purchase #3	$154.39	10.622%	$170.7893	$170.79	$170.80	$170.80
Purchase #4	$240.63	6.295%	$255.7777	$255.78	$255.80	$255.80
Purchase #5	$82.81	8.439%	$89.7983	$89.80	$89.80	$89.80
Purchase #6	$83.57	6.110%	$88.6761	$88.68	$88.70	$88.70
Purchase #7	$216.30	6.688%	$230.7661	$230.77	$230.75	$230.80
7 purchase totals =	$943.91		$1,019.5607	$1,019.58	$1,019.60	$1,019.70