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	$56.27	5.851%	$59.5624	$59.56	$59.55	$59.60
Purchase #2	$92.60	9.203%	$101.122	$101.12	$101.10	$101.10
Purchase #3	$116.64	13.162%	$131.9922	$131.99	$132.00	$132.00
Purchase #4	$168.81	4.673%	$176.6985	$176.70	$176.70	$176.70
Purchase #5	$52.37	4.125%	$54.5303	$54.53	$54.55	$54.50
Purchase #6	$77.76	5.505%	$82.0407	$82.04	$82.05	$82.00
Purchase #7	$199.47	7.595%	$214.6197	$214.62	$214.60	$214.60
7 purchase totals =	$763.92		$820.5658	$820.56	$820.55	$820.50