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	$45.36	6.223%	$48.1828	$48.18	$48.20	$48.20
Purchase #2	$100.74	11.149%	$111.9715	$111.97	$111.95	$112.00
Purchase #3	$131.50	10.676%	$145.5389	$145.54	$145.55	$145.50
Purchase #4	$82.33	6.336%	$87.5464	$87.55	$87.55	$87.50
Purchase #5	$52.74	3.317%	$54.4894	$54.49	$54.50	$54.50
Purchase #6	$98.65	10.561%	$109.0684	$109.07	$109.05	$109.10
Purchase #7	$128.29	8.398%	$139.0638	$139.06	$139.05	$139.10
7 purchase totals =	$639.61		$695.8612	$695.86	$695.85	$695.90