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	$205.71	6.368%	$218.8096	$218.81	$218.80	$218.80
Purchase #2	$143.38	7.324%	$153.8812	$153.88	$153.90	$153.90
Purchase #3	$172.45	13.418%	$195.5893	$195.59	$195.60	$195.60
Purchase #4	$120.61	12.305%	$135.4511	$135.45	$135.45	$135.50
Purchase #5	$237.58	7.590%	$255.6123	$255.61	$255.60	$255.60
Purchase #6	$206.63	10.450%	$228.2228	$228.22	$228.20	$228.20
Purchase #7	$102.45	10.163%	$112.862	$112.86	$112.85	$112.90
7 purchase totals =	$1,188.81		$1,300.4283	$1,300.42	$1,300.40	$1,300.50