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	$19.25	3.683%	$19.959	$19.96	$19.95	$20.00
Purchase #2	$55.96	12.762%	$63.1016	$63.10	$63.10	$63.10
Purchase #3	$152.45	9.685%	$167.2148	$167.21	$167.20	$167.20
Purchase #4	$237.70	3.283%	$245.5037	$245.50	$245.50	$245.50
Purchase #5	$228.78	11.264%	$254.5498	$254.55	$254.55	$254.50
Purchase #6	$43.47	4.549%	$45.4475	$45.45	$45.45	$45.40
Purchase #7	$38.60	4.342%	$40.276	$40.28	$40.30	$40.30
7 purchase totals =	$776.21		$836.0524	$836.05	$836.05	$836.00