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	$249.78	11.797%	$279.2465	$279.25	$279.25	$279.20
Purchase #2	$48.57	6.862%	$51.9029	$51.90	$51.90	$51.90
Purchase #3	$178.35	3.830%	$185.1808	$185.18	$185.20	$185.20
Purchase #4	$98.92	13.277%	$112.0536	$112.05	$112.05	$112.10
Purchase #5	$117.34	9.456%	$128.4357	$128.44	$128.45	$128.40
Purchase #6	$58.41	11.236%	$64.9729	$64.97	$64.95	$65.00
Purchase #7	$168.55	10.173%	$185.6966	$185.70	$185.70	$185.70
7 purchase totals =	$919.92		$1,007.4890	$1,007.49	$1,007.50	$1,007.50