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	$226.57	13.264%	$256.6222	$256.62	$256.60	$256.60
Purchase #2	$176.46	4.451%	$184.3142	$184.31	$184.30	$184.30
Purchase #3	$186.28	5.612%	$196.734	$196.73	$196.75	$196.70
Purchase #4	$97.67	5.741%	$103.2772	$103.28	$103.30	$103.30
Purchase #5	$181.65	11.716%	$202.9321	$202.93	$202.95	$202.90
Purchase #6	$35.28	4.641%	$36.9173	$36.92	$36.90	$36.90
Purchase #7	$127.45	11.863%	$142.5694	$142.57	$142.55	$142.60
7 purchase totals =	$1,031.36		$1,123.3664	$1,123.36	$1,123.35	$1,123.30