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	$236.48	9.818%	$259.6976	$259.70	$259.70	$259.70
Purchase #2	$68.40	5.412%	$72.1018	$72.10	$72.10	$72.10
Purchase #3	$54.81	8.873%	$59.6733	$59.67	$59.65	$59.70
Purchase #4	$166.35	12.268%	$186.7578	$186.76	$186.75	$186.80
Purchase #5	$32.75	13.584%	$37.1988	$37.20	$37.20	$37.20
Purchase #6	$17.59	10.501%	$19.4371	$19.44	$19.45	$19.40
Purchase #7	$11.88	6.124%	$12.6075	$12.61	$12.60	$12.60
7 purchase totals =	$588.26		$647.4739	$647.48	$647.45	$647.50