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	$134.37	10.179%	$148.0475	$148.05	$148.05	$148.00
Purchase #2	$106.40	10.376%	$117.4401	$117.44	$117.45	$117.40
Purchase #3	$169.54	5.528%	$178.9122	$178.91	$178.90	$178.90
Purchase #4	$167.38	13.839%	$190.5437	$190.54	$190.55	$190.50
Purchase #5	$35.45	10.405%	$39.1386	$39.14	$39.15	$39.10
Purchase #6	$132.46	6.685%	$141.315	$141.32	$141.30	$141.30
Purchase #7	$22.46	6.301%	$23.8752	$23.88	$23.90	$23.90
7 purchase totals =	$768.06		$839.2723	$839.28	$839.30	$839.10