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	$153.45	9.366%	$167.8221	$167.82	$167.80	$167.80
Purchase #2	$17.65	3.726%	$18.3076	$18.31	$18.30	$18.30
Purchase #3	$101.56	6.470%	$108.1309	$108.13	$108.15	$108.10
Purchase #4	$13.33	13.594%	$15.1421	$15.14	$15.15	$15.10
Purchase #5	$91.50	13.683%	$104.0199	$104.02	$104.00	$104.00
Purchase #6	$101.40	13.212%	$114.797	$114.80	$114.80	$114.80
Purchase #7	$82.61	9.807%	$90.7116	$90.71	$90.70	$90.70
7 purchase totals =	$561.50		$618.9312	$618.93	$618.90	$618.80