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	$6.77	6.222%	$7.1912	$7.19	$7.20	$7.20
Purchase #2	$97.70	9.495%	$106.9766	$106.98	$107.00	$107.00
Purchase #3	$18.76	12.580%	$21.12	$21.12	$21.10	$21.10
Purchase #4	$46.45	5.198%	$48.8645	$48.86	$48.85	$48.90
Purchase #5	$118.68	7.450%	$127.5217	$127.52	$127.50	$127.50
Purchase #6	$72.92	12.858%	$82.2961	$82.30	$82.30	$82.30
Purchase #7	$50.52	4.836%	$52.9631	$52.96	$52.95	$53.00
7 purchase totals =	$411.80		$446.9332	$446.93	$446.90	$447.00