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	$144.52	6.851%	$154.4211	$154.42	$154.40	$154.40
Purchase #2	$223.54	9.218%	$244.1459	$244.15	$244.15	$244.10
Purchase #3	$52.99	6.600%	$56.4873	$56.49	$56.50	$56.50
Purchase #4	$11.47	13.444%	$13.012	$13.01	$13.00	$13.00
Purchase #5	$104.46	4.231%	$108.8797	$108.88	$108.90	$108.90
Purchase #6	$158.31	9.705%	$173.674	$173.67	$173.65	$173.70
Purchase #7	$80.64	13.230%	$91.3087	$91.31	$91.30	$91.30
7 purchase totals =	$775.93		$841.9287	$841.93	$841.90	$841.90