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	$20.72	4.134%	$21.5766	$21.58	$21.60	$21.60
Purchase #2	$95.30	4.832%	$99.9049	$99.90	$99.90	$99.90
Purchase #3	$135.52	9.360%	$148.2047	$148.20	$148.20	$148.20
Purchase #4	$132.82	4.678%	$139.0333	$139.03	$139.05	$139.00
Purchase #5	$80.81	11.653%	$90.2268	$90.23	$90.25	$90.20
Purchase #6	$68.86	12.708%	$77.6107	$77.61	$77.60	$77.60
Purchase #7	$64.39	10.720%	$71.2926	$71.29	$71.30	$71.30
7 purchase totals =	$598.42		$647.8496	$647.84	$647.90	$647.80