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	$139.80	4.582%	$146.2056	$146.21	$146.20	$146.20
Purchase #2	$25.38	7.151%	$27.1949	$27.19	$27.20	$27.20
Purchase #3	$39.61	9.782%	$43.4847	$43.48	$43.50	$43.50
Purchase #4	$147.51	11.596%	$164.6153	$164.62	$164.60	$164.60
Purchase #5	$111.35	10.537%	$123.0829	$123.08	$123.10	$123.10
Purchase #6	$189.61	13.255%	$214.7428	$214.74	$214.75	$214.70
Purchase #7	$157.25	10.208%	$173.3021	$173.30	$173.30	$173.30
7 purchase totals =	$810.51		$892.6283	$892.62	$892.65	$892.60