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	$241.86	6.326%	$257.1601	$257.16	$257.15	$257.20
Purchase #2	$184.80	6.759%	$197.2906	$197.29	$197.30	$197.30
Purchase #3	$151.25	10.540%	$167.1918	$167.19	$167.20	$167.20
Purchase #4	$175.72	9.228%	$191.9354	$191.94	$191.95	$191.90
Purchase #5	$62.74	6.629%	$66.899	$66.90	$66.90	$66.90
Purchase #6	$24.97	10.387%	$27.5636	$27.56	$27.55	$27.60
Purchase #7	$105.95	5.523%	$111.8016	$111.80	$111.80	$111.80
7 purchase totals =	$947.29		$1,019.8421	$1,019.84	$1,019.85	$1,019.90