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	$25.53	11.700%	$28.517	$28.52	$28.50	$28.50
Purchase #2	$79.88	10.332%	$88.1332	$88.13	$88.15	$88.10
Purchase #3	$60.72	6.425%	$64.6213	$64.62	$64.60	$64.60
Purchase #4	$82.99	7.854%	$89.508	$89.51	$89.50	$89.50
Purchase #5	$228.51	13.724%	$259.8707	$259.87	$259.85	$259.90
Purchase #6	$113.68	7.720%	$122.4561	$122.46	$122.45	$122.50
Purchase #7	$173.54	9.267%	$189.622	$189.62	$189.60	$189.60
7 purchase totals =	$764.85		$842.7283	$842.73	$842.65	$842.70