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	$163.41	9.836%	$179.483	$179.48	$179.50	$179.50
Purchase #2	$225.68	13.128%	$255.3073	$255.31	$255.30	$255.30
Purchase #3	$133.56	4.255%	$139.243	$139.24	$139.25	$139.20
Purchase #4	$73.43	11.197%	$81.652	$81.65	$81.65	$81.70
Purchase #5	$139.35	13.523%	$158.1943	$158.19	$158.20	$158.20
Purchase #6	$44.48	3.734%	$46.1409	$46.14	$46.15	$46.10
Purchase #7	$29.69	9.131%	$32.401	$32.40	$32.40	$32.40
7 purchase totals =	$809.60		$892.4215	$892.41	$892.45	$892.40