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	$34.74	12.641%	$39.1315	$39.13	$39.15	$39.10
Purchase #2	$178.39	5.782%	$188.7045	$188.70	$188.70	$188.70
Purchase #3	$148.75	12.671%	$167.5981	$167.60	$167.60	$167.60
Purchase #4	$172.64	13.765%	$196.4039	$196.40	$196.40	$196.40
Purchase #5	$184.26	4.404%	$192.3748	$192.37	$192.35	$192.40
Purchase #6	$37.71	8.523%	$40.924	$40.92	$40.90	$40.90
Purchase #7	$227.82	4.692%	$238.5093	$238.51	$238.50	$238.50
7 purchase totals =	$984.31		$1,063.6461	$1,063.63	$1,063.60	$1,063.60