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	$151.88	8.778%	$165.212	$165.21	$165.20	$165.20
Purchase #2	$141.96	7.366%	$152.4168	$152.42	$152.40	$152.40
Purchase #3	$224.70	13.153%	$254.2548	$254.25	$254.25	$254.30
Purchase #4	$180.52	7.605%	$194.2485	$194.25	$194.25	$194.20
Purchase #5	$137.25	3.407%	$141.9261	$141.93	$141.95	$141.90
Purchase #6	$237.50	11.410%	$264.5988	$264.60	$264.60	$264.60
Purchase #7	$66.82	8.412%	$72.4409	$72.44	$72.45	$72.40
7 purchase totals =	$1,140.63		$1,245.0979	$1,245.10	$1,245.10	$1,245.00