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	$165.99	13.509%	$188.4136	$188.41	$188.40	$188.40
Purchase #2	$116.32	12.852%	$131.2694	$131.27	$131.25	$131.30
Purchase #3	$163.38	7.813%	$176.1449	$176.14	$176.15	$176.10
Purchase #4	$61.88	4.428%	$64.62	$64.62	$64.60	$64.60
Purchase #5	$64.41	3.588%	$66.721	$66.72	$66.70	$66.70
Purchase #6	$86.86	3.554%	$89.947	$89.95	$89.95	$89.90
Purchase #7	$172.75	7.102%	$185.0187	$185.02	$185.00	$185.00
7 purchase totals =	$831.59		$902.1346	$902.13	$902.05	$902.00