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	$86.42	3.355%	$89.3194	$89.32	$89.30	$89.30
Purchase #2	$175.61	11.660%	$196.0861	$196.09	$196.10	$196.10
Purchase #3	$154.80	12.355%	$173.9255	$173.93	$173.95	$173.90
Purchase #4	$206.52	6.313%	$219.5576	$219.56	$219.55	$219.60
Purchase #5	$205.66	13.667%	$233.7676	$233.77	$233.75	$233.80
Purchase #6	$82.89	12.693%	$93.4112	$93.41	$93.40	$93.40
Purchase #7	$157.99	3.441%	$163.4264	$163.43	$163.45	$163.40
7 purchase totals =	$1,069.89		$1,169.4938	$1,169.51	$1,169.50	$1,169.50