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	$14.89	6.207%	$15.8142	$15.81	$15.80	$15.80
Purchase #2	$160.30	7.523%	$172.3594	$172.36	$172.35	$172.40
Purchase #3	$218.60	7.420%	$234.8201	$234.82	$234.80	$234.80
Purchase #4	$153.93	5.832%	$162.9072	$162.91	$162.90	$162.90
Purchase #5	$45.91	5.456%	$48.4148	$48.41	$48.40	$48.40
Purchase #6	$98.91	4.830%	$103.6874	$103.69	$103.70	$103.70
Purchase #7	$108.88	9.758%	$119.5045	$119.50	$119.50	$119.50
7 purchase totals =	$801.42		$857.5076	$857.50	$857.45	$857.50