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	$111.91	6.144%	$118.7858	$118.79	$118.80	$118.80
Purchase #2	$34.29	13.717%	$38.9936	$38.99	$39.00	$39.00
Purchase #3	$171.67	4.810%	$179.9273	$179.93	$179.95	$179.90
Purchase #4	$27.93	3.412%	$28.883	$28.88	$28.90	$28.90
Purchase #5	$178.58	11.599%	$199.2935	$199.29	$199.30	$199.30
Purchase #6	$66.26	7.747%	$71.3932	$71.39	$71.40	$71.40
Purchase #7	$97.67	13.814%	$111.1621	$111.16	$111.15	$111.20
7 purchase totals =	$688.31		$748.4385	$748.43	$748.50	$748.50