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	$42.61	10.577%	$47.1169	$47.12	$47.10	$47.10
Purchase #2	$175.90	5.384%	$185.3705	$185.37	$185.35	$185.40
Purchase #3	$129.33	9.193%	$141.2193	$141.22	$141.20	$141.20
Purchase #4	$98.53	7.408%	$105.8291	$105.83	$105.85	$105.80
Purchase #5	$103.52	7.414%	$111.195	$111.20	$111.20	$111.20
Purchase #6	$231.92	12.450%	$260.794	$260.79	$260.80	$260.80
Purchase #7	$132.25	4.186%	$137.786	$137.79	$137.80	$137.80
7 purchase totals =	$914.06		$989.3108	$989.32	$989.30	$989.30