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	$100.72	5.579%	$106.3392	$106.34	$106.35	$106.30
Purchase #2	$78.68	4.632%	$82.3245	$82.32	$82.30	$82.30
Purchase #3	$132.89	9.282%	$145.2248	$145.22	$145.20	$145.20
Purchase #4	$110.33	3.421%	$114.1044	$114.10	$114.10	$114.10
Purchase #5	$158.43	5.864%	$167.7203	$167.72	$167.70	$167.70
Purchase #6	$142.76	4.711%	$149.4854	$149.49	$149.50	$149.50
Purchase #7	$116.45	9.273%	$127.2484	$127.25	$127.25	$127.20
7 purchase totals =	$840.26		$892.4470	$892.44	$892.40	$892.30