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	$89.67	9.728%	$98.3931	$98.39	$98.40	$98.40
Purchase #2	$108.71	13.275%	$123.1413	$123.14	$123.15	$123.10
Purchase #3	$112.56	12.176%	$126.2653	$126.27	$126.25	$126.30
Purchase #4	$158.82	3.589%	$164.52	$164.52	$164.50	$164.50
Purchase #5	$161.45	10.864%	$178.9899	$178.99	$179.00	$179.00
Purchase #6	$217.82	6.137%	$231.1876	$231.19	$231.20	$231.20
Purchase #7	$137.48	8.662%	$149.3885	$149.39	$149.40	$149.40
7 purchase totals =	$986.51		$1,071.8857	$1,071.89	$1,071.90	$1,071.90