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	$11.67	6.242%	$12.3984	$12.40	$12.40	$12.40
Purchase #2	$179.49	8.364%	$194.5025	$194.50	$194.50	$194.50
Purchase #3	$126.72	13.393%	$143.6916	$143.69	$143.70	$143.70
Purchase #4	$85.56	4.441%	$89.3597	$89.36	$89.35	$89.40
Purchase #5	$145.55	6.677%	$155.2684	$155.27	$155.25	$155.30
Purchase #6	$227.82	11.252%	$253.4543	$253.45	$253.45	$253.50
Purchase #7	$238.87	12.624%	$269.0249	$269.02	$269.00	$269.00
7 purchase totals =	$1,015.68		$1,117.6998	$1,117.69	$1,117.65	$1,117.80