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	$95.51	5.163%	$100.4412	$100.44	$100.45	$100.40
Purchase #2	$139.69	7.462%	$150.1137	$150.11	$150.10	$150.10
Purchase #3	$126.35	10.548%	$139.6774	$139.68	$139.70	$139.70
Purchase #4	$165.99	5.750%	$175.5344	$175.53	$175.55	$175.50
Purchase #5	$42.75	5.603%	$45.1453	$45.15	$45.15	$45.10
Purchase #6	$54.97	7.595%	$59.145	$59.15	$59.15	$59.10
Purchase #7	$213.27	12.719%	$240.3958	$240.40	$240.40	$240.40
7 purchase totals =	$838.53		$910.4528	$910.46	$910.50	$910.30