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	$24.47	13.706%	$27.8239	$27.82	$27.80	$27.80
Purchase #2	$200.81	10.839%	$222.5758	$222.58	$222.60	$222.60
Purchase #3	$83.91	5.528%	$88.5485	$88.55	$88.55	$88.50
Purchase #4	$171.68	9.651%	$188.2488	$188.25	$188.25	$188.20
Purchase #5	$76.41	9.423%	$83.6101	$83.61	$83.60	$83.60
Purchase #6	$166.69	10.425%	$184.0674	$184.07	$184.05	$184.10
Purchase #7	$220.33	9.504%	$241.2702	$241.27	$241.25	$241.30
7 purchase totals =	$944.30		$1,036.1447	$1,036.15	$1,036.10	$1,036.10