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	$149.47	5.837%	$158.1946	$158.19	$158.20	$158.20
Purchase #2	$187.79	10.262%	$207.061	$207.06	$207.05	$207.10
Purchase #3	$59.63	6.533%	$63.5256	$63.53	$63.55	$63.50
Purchase #4	$245.90	3.818%	$255.2885	$255.29	$255.30	$255.30
Purchase #5	$118.33	7.620%	$127.3467	$127.35	$127.35	$127.30
Purchase #6	$218.65	10.545%	$241.7066	$241.71	$241.70	$241.70
Purchase #7	$156.33	10.112%	$172.1381	$172.14	$172.15	$172.10
7 purchase totals =	$1,136.10		$1,225.2611	$1,225.27	$1,225.30	$1,225.20