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	$137.40	6.123%	$145.813	$145.81	$145.80	$145.80
Purchase #2	$186.75	11.533%	$208.2879	$208.29	$208.30	$208.30
Purchase #3	$48.29	10.454%	$53.3382	$53.34	$53.35	$53.30
Purchase #4	$47.30	6.765%	$50.4998	$50.50	$50.50	$50.50
Purchase #5	$51.96	7.682%	$55.9516	$55.95	$55.95	$56.00
Purchase #6	$103.42	7.339%	$111.01	$111.01	$111.00	$111.00
Purchase #7	$221.46	4.836%	$232.1698	$232.17	$232.15	$232.20
7 purchase totals =	$796.58		$857.0703	$857.07	$857.05	$857.10