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	$228.85	8.496%	$248.2931	$248.29	$248.30	$248.30
Purchase #2	$155.80	10.633%	$172.3662	$172.37	$172.35	$172.40
Purchase #3	$160.35	7.429%	$172.2624	$172.26	$172.25	$172.30
Purchase #4	$245.75	7.588%	$264.3975	$264.40	$264.40	$264.40
Purchase #5	$169.77	4.663%	$177.6864	$177.69	$177.70	$177.70
Purchase #6	$123.28	13.339%	$139.7243	$139.72	$139.70	$139.70
Purchase #7	$92.79	12.719%	$104.592	$104.59	$104.60	$104.60
7 purchase totals =	$1,176.59		$1,279.3219	$1,279.32	$1,279.30	$1,279.40