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	$79.45	13.501%	$90.1765	$90.18	$90.20	$90.20
Purchase #2	$45.82	13.850%	$52.1661	$52.17	$52.15	$52.20
Purchase #3	$54.66	3.659%	$56.66	$56.66	$56.65	$56.70
Purchase #4	$68.58	4.206%	$71.4645	$71.46	$71.45	$71.50
Purchase #5	$235.72	5.140%	$247.836	$247.84	$247.85	$247.80
Purchase #6	$95.47	5.656%	$100.8698	$100.87	$100.85	$100.90
Purchase #7	$9.51	12.506%	$10.6993	$10.70	$10.70	$10.70
7 purchase totals =	$589.21		$629.8722	$629.88	$629.85	$630.00