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	$234.70	6.358%	$249.6222	$249.62	$249.60	$249.60
Purchase #2	$51.38	5.723%	$54.3205	$54.32	$54.30	$54.30
Purchase #3	$131.93	8.793%	$143.5306	$143.53	$143.55	$143.50
Purchase #4	$181.65	13.562%	$206.2854	$206.29	$206.30	$206.30
Purchase #5	$195.47	13.762%	$222.3706	$222.37	$222.35	$222.40
Purchase #6	$59.42	11.449%	$66.223	$66.22	$66.20	$66.20
Purchase #7	$179.95	8.295%	$194.8769	$194.88	$194.90	$194.90
7 purchase totals =	$1,034.50		$1,137.2292	$1,137.23	$1,137.20	$1,137.20