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	$60.89	9.444%	$66.6405	$66.64	$66.65	$66.60
Purchase #2	$86.61	3.863%	$89.9557	$89.96	$89.95	$90.00
Purchase #3	$49.28	12.733%	$55.5548	$55.55	$55.55	$55.60
Purchase #4	$229.99	6.358%	$244.6128	$244.61	$244.60	$244.60
Purchase #5	$119.56	6.856%	$127.757	$127.76	$127.75	$127.80
Purchase #6	$195.35	10.358%	$215.5844	$215.58	$215.60	$215.60
Purchase #7	$40.93	3.622%	$42.4125	$42.41	$42.40	$42.40
7 purchase totals =	$782.61		$842.5177	$842.51	$842.50	$842.60