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	$158.80	12.488%	$178.6309	$178.63	$178.65	$178.60
Purchase #2	$205.38	3.597%	$212.7675	$212.77	$212.75	$212.80
Purchase #3	$31.52	11.353%	$35.0985	$35.10	$35.10	$35.10
Purchase #4	$105.26	5.613%	$111.1682	$111.17	$111.15	$111.20
Purchase #5	$61.41	7.722%	$66.1521	$66.15	$66.15	$66.20
Purchase #6	$147.33	7.721%	$158.7053	$158.71	$158.70	$158.70
Purchase #7	$61.47	6.316%	$65.3524	$65.35	$65.35	$65.40
7 purchase totals =	$771.17		$827.8749	$827.88	$827.85	$828.00