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	$171.37	9.758%	$188.0923	$188.09	$188.10	$188.10
Purchase #2	$102.30	9.239%	$111.7515	$111.75	$111.75	$111.80
Purchase #3	$37.88	6.508%	$40.3452	$40.35	$40.35	$40.30
Purchase #4	$238.54	8.346%	$258.4485	$258.45	$258.45	$258.40
Purchase #5	$157.81	11.542%	$176.0244	$176.02	$176.00	$176.00
Purchase #6	$6.78	6.318%	$7.2084	$7.21	$7.20	$7.20
Purchase #7	$46.83	10.135%	$51.5762	$51.58	$51.60	$51.60
7 purchase totals =	$761.51		$833.4465	$833.45	$833.45	$833.40