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	$199.94	6.145%	$212.2263	$212.23	$212.25	$212.20
Purchase #2	$241.27	10.468%	$266.5261	$266.53	$266.55	$266.50
Purchase #3	$179.25	8.517%	$194.5167	$194.52	$194.50	$194.50
Purchase #4	$239.29	4.743%	$250.6395	$250.64	$250.65	$250.60
Purchase #5	$234.53	13.846%	$267.003	$267.00	$267.00	$267.00
Purchase #6	$113.83	11.724%	$127.1754	$127.18	$127.20	$127.20
Purchase #7	$161.77	12.843%	$182.5461	$182.55	$182.55	$182.50
7 purchase totals =	$1,369.88		$1,500.6331	$1,500.65	$1,500.70	$1,500.50