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	$18.71	3.228%	$19.314	$19.31	$19.30	$19.30
Purchase #2	$37.53	3.602%	$38.8818	$38.88	$38.90	$38.90
Purchase #3	$138.52	3.721%	$143.6743	$143.67	$143.65	$143.70
Purchase #4	$54.50	4.210%	$56.7945	$56.79	$56.80	$56.80
Purchase #5	$18.82	5.341%	$19.8252	$19.83	$19.85	$19.80
Purchase #6	$89.75	10.390%	$99.075	$99.08	$99.10	$99.10
Purchase #7	$47.71	8.209%	$51.6265	$51.63	$51.65	$51.60
7 purchase totals =	$405.54		$429.1913	$429.19	$429.25	$429.20