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	$79.82	12.255%	$89.6019	$89.60	$89.60	$89.60
Purchase #2	$49.49	13.546%	$56.1939	$56.19	$56.20	$56.20
Purchase #3	$50.61	4.107%	$52.6886	$52.69	$52.70	$52.70
Purchase #4	$181.35	6.675%	$193.4551	$193.46	$193.45	$193.50
Purchase #5	$37.52	3.380%	$38.7882	$38.79	$38.80	$38.80
Purchase #6	$34.59	11.578%	$38.5948	$38.59	$38.60	$38.60
Purchase #7	$198.58	4.130%	$206.7814	$206.78	$206.80	$206.80
7 purchase totals =	$631.96		$676.1039	$676.10	$676.15	$676.20