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	$91.65	13.218%	$103.7643	$103.76	$103.75	$103.80
Purchase #2	$34.77	10.842%	$38.5398	$38.54	$38.55	$38.50
Purchase #3	$119.85	10.320%	$132.2185	$132.22	$132.20	$132.20
Purchase #4	$64.64	11.821%	$72.2811	$72.28	$72.30	$72.30
Purchase #5	$49.28	9.145%	$53.7867	$53.79	$53.80	$53.80
Purchase #6	$47.67	13.753%	$54.2261	$54.23	$54.25	$54.20
Purchase #7	$236.45	7.447%	$254.0584	$254.06	$254.05	$254.10
7 purchase totals =	$644.31		$708.8749	$708.88	$708.90	$708.90