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	$202.82	13.838%	$230.8862	$230.89	$230.90	$230.90
Purchase #2	$115.39	11.262%	$128.3852	$128.39	$128.40	$128.40
Purchase #3	$202.61	13.601%	$230.167	$230.17	$230.15	$230.20
Purchase #4	$104.60	4.531%	$109.3394	$109.34	$109.35	$109.30
Purchase #5	$246.74	4.140%	$256.955	$256.96	$256.95	$257.00
Purchase #6	$224.81	13.809%	$255.854	$255.85	$255.85	$255.90
Purchase #7	$134.93	9.251%	$147.4124	$147.41	$147.40	$147.40
7 purchase totals =	$1,231.90		$1,358.9992	$1,359.01	$1,359.00	$1,359.10