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	$232.48	3.147%	$239.7961	$239.80	$239.80	$239.80
Purchase #2	$82.94	7.423%	$89.0966	$89.10	$89.10	$89.10
Purchase #3	$143.67	5.536%	$151.6236	$151.62	$151.60	$151.60
Purchase #4	$56.59	11.544%	$63.1227	$63.12	$63.10	$63.10
Purchase #5	$37.59	12.128%	$42.1489	$42.15	$42.15	$42.10
Purchase #6	$107.30	12.117%	$120.3015	$120.30	$120.30	$120.30
Purchase #7	$171.36	13.375%	$194.2794	$194.28	$194.30	$194.30
7 purchase totals =	$831.93		$900.3688	$900.37	$900.35	$900.30