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	$172.59	8.857%	$187.8763	$187.88	$187.90	$187.90
Purchase #2	$144.39	6.535%	$153.8259	$153.83	$153.85	$153.80
Purchase #3	$54.59	8.378%	$59.1636	$59.16	$59.15	$59.20
Purchase #4	$14.78	4.750%	$15.4821	$15.48	$15.50	$15.50
Purchase #5	$56.25	6.141%	$59.7043	$59.70	$59.70	$59.70
Purchase #6	$105.86	9.872%	$116.3105	$116.31	$116.30	$116.30
Purchase #7	$202.29	13.643%	$229.8884	$229.89	$229.90	$229.90
7 purchase totals =	$750.75		$822.2511	$822.25	$822.30	$822.30