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	$10.51	5.468%	$11.0847	$11.08	$11.10	$11.10
Purchase #2	$179.92	3.590%	$186.3791	$186.38	$186.40	$186.40
Purchase #3	$179.83	3.810%	$186.6815	$186.68	$186.70	$186.70
Purchase #4	$13.70	11.611%	$15.2907	$15.29	$15.30	$15.30
Purchase #5	$80.81	10.433%	$89.2409	$89.24	$89.25	$89.20
Purchase #6	$176.49	7.778%	$190.2174	$190.22	$190.20	$190.20
Purchase #7	$152.38	9.860%	$167.4047	$167.40	$167.40	$167.40
7 purchase totals =	$793.64		$846.2990	$846.29	$846.35	$846.30