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	$236.31	8.412%	$256.1884	$256.19	$256.20	$256.20
Purchase #2	$219.39	7.624%	$236.1163	$236.12	$236.10	$236.10
Purchase #3	$75.82	8.863%	$82.5399	$82.54	$82.55	$82.50
Purchase #4	$122.29	13.779%	$139.1403	$139.14	$139.15	$139.10
Purchase #5	$143.31	12.196%	$160.7881	$160.79	$160.80	$160.80
Purchase #6	$147.85	7.360%	$158.7318	$158.73	$158.75	$158.70
Purchase #7	$241.28	10.730%	$267.1693	$267.17	$267.15	$267.20
7 purchase totals =	$1,186.25		$1,300.6741	$1,300.68	$1,300.70	$1,300.60