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	$156.69	7.106%	$167.8244	$167.82	$167.80	$167.80
Purchase #2	$138.40	12.275%	$155.3886	$155.39	$155.40	$155.40
Purchase #3	$165.31	9.171%	$180.4706	$180.47	$180.45	$180.50
Purchase #4	$36.32	7.161%	$38.9209	$38.92	$38.90	$38.90
Purchase #5	$205.95	5.163%	$216.5832	$216.58	$216.60	$216.60
Purchase #6	$198.85	6.337%	$211.4511	$211.45	$211.45	$211.50
Purchase #7	$12.66	4.626%	$13.2457	$13.25	$13.25	$13.20
7 purchase totals =	$914.18		$983.8845	$983.88	$983.85	$983.90