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	$38.99	8.351%	$42.2461	$42.25	$42.25	$42.20
Purchase #2	$104.81	11.353%	$116.7091	$116.71	$116.70	$116.70
Purchase #3	$225.96	13.108%	$255.5788	$255.58	$255.60	$255.60
Purchase #4	$82.38	9.616%	$90.3017	$90.30	$90.30	$90.30
Purchase #5	$220.60	10.746%	$244.3057	$244.31	$244.30	$244.30
Purchase #6	$202.46	6.328%	$215.2717	$215.27	$215.25	$215.30
Purchase #7	$189.38	13.565%	$215.0694	$215.07	$215.05	$215.10
7 purchase totals =	$1,064.58		$1,179.4825	$1,179.49	$1,179.45	$1,179.50