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	$99.50	11.704%	$111.1455	$111.15	$111.15	$111.10
Purchase #2	$181.52	13.106%	$205.31	$205.31	$205.30	$205.30
Purchase #3	$79.76	8.687%	$86.6888	$86.69	$86.70	$86.70
Purchase #4	$16.36	10.596%	$18.0935	$18.09	$18.10	$18.10
Purchase #5	$157.31	10.282%	$173.4846	$173.48	$173.50	$173.50
Purchase #6	$237.64	9.796%	$260.9192	$260.92	$260.90	$260.90
Purchase #7	$62.46	3.746%	$64.7998	$64.80	$64.80	$64.80
7 purchase totals =	$834.55		$920.4414	$920.44	$920.45	$920.40