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	$71.76	8.426%	$77.8065	$77.81	$77.80	$77.80
Purchase #2	$29.79	10.436%	$32.8989	$32.90	$32.90	$32.90
Purchase #3	$96.91	11.207%	$107.7707	$107.77	$107.75	$107.80
Purchase #4	$215.55	7.250%	$231.1774	$231.18	$231.20	$231.20
Purchase #5	$124.90	13.268%	$141.4717	$141.47	$141.45	$141.50
Purchase #6	$88.31	11.184%	$98.1866	$98.19	$98.20	$98.20
Purchase #7	$174.71	12.536%	$196.6116	$196.61	$196.60	$196.60
7 purchase totals =	$801.93		$885.9234	$885.93	$885.90	$886.00