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	$52.47	13.629%	$59.6211	$59.62	$59.60	$59.60
Purchase #2	$37.61	7.165%	$40.3048	$40.30	$40.30	$40.30
Purchase #3	$65.40	7.839%	$70.5267	$70.53	$70.55	$70.50
Purchase #4	$102.72	5.625%	$108.498	$108.50	$108.50	$108.50
Purchase #5	$66.43	7.204%	$71.2156	$71.22	$71.20	$71.20
Purchase #6	$123.54	8.465%	$133.9977	$134.00	$134.00	$134.00
Purchase #7	$178.30	5.733%	$188.5219	$188.52	$188.50	$188.50
7 purchase totals =	$626.47		$672.6858	$672.69	$672.65	$672.60