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	$15.56	5.852%	$16.4706	$16.47	$16.45	$16.50
Purchase #2	$79.25	13.426%	$89.8901	$89.89	$89.90	$89.90
Purchase #3	$98.46	11.390%	$109.6746	$109.67	$109.65	$109.70
Purchase #4	$145.72	13.646%	$165.605	$165.61	$165.60	$165.60
Purchase #5	$34.73	11.433%	$38.7007	$38.70	$38.70	$38.70
Purchase #6	$123.98	3.724%	$128.597	$128.60	$128.60	$128.60
Purchase #7	$11.34	10.584%	$12.5402	$12.54	$12.55	$12.50
7 purchase totals =	$509.04		$561.4782	$561.48	$561.45	$561.50