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	$19.49	13.588%	$22.1383	$22.14	$22.15	$22.10
Purchase #2	$161.81	5.348%	$170.4636	$170.46	$170.45	$170.50
Purchase #3	$109.55	9.422%	$119.8718	$119.87	$119.85	$119.90
Purchase #4	$212.47	6.110%	$225.4519	$225.45	$225.45	$225.50
Purchase #5	$137.88	9.429%	$150.8807	$150.88	$150.90	$150.90
Purchase #6	$84.35	7.518%	$90.6914	$90.69	$90.70	$90.70
Purchase #7	$171.35	10.466%	$189.2835	$189.28	$189.30	$189.30
7 purchase totals =	$896.90		$968.7812	$968.77	$968.80	$968.90