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	$70.64	12.678%	$79.5957	$79.60	$79.60	$79.60
Purchase #2	$108.73	10.835%	$120.5109	$120.51	$120.50	$120.50
Purchase #3	$105.71	6.349%	$112.4215	$112.42	$112.40	$112.40
Purchase #4	$29.79	8.628%	$32.3603	$32.36	$32.35	$32.40
Purchase #5	$78.75	13.588%	$89.4506	$89.45	$89.45	$89.50
Purchase #6	$221.73	7.686%	$238.7722	$238.77	$238.75	$238.80
Purchase #7	$194.81	4.364%	$203.3115	$203.31	$203.30	$203.30
7 purchase totals =	$810.16		$876.4227	$876.42	$876.35	$876.50