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	$17.93	3.809%	$18.613	$18.61	$18.60	$18.60
Purchase #2	$111.96	6.557%	$119.3012	$119.30	$119.30	$119.30
Purchase #3	$226.39	3.569%	$234.4699	$234.47	$234.45	$234.50
Purchase #4	$58.65	6.321%	$62.3573	$62.36	$62.35	$62.40
Purchase #5	$198.35	13.503%	$225.1332	$225.13	$225.15	$225.10
Purchase #6	$25.38	6.630%	$27.0627	$27.06	$27.05	$27.10
Purchase #7	$65.52	10.215%	$72.2129	$72.21	$72.20	$72.20
7 purchase totals =	$704.18		$759.1502	$759.14	$759.10	$759.20