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	$17.40	3.612%	$18.0285	$18.03	$18.05	$18.00
Purchase #2	$8.25	4.273%	$8.6025	$8.60	$8.60	$8.60
Purchase #3	$214.43	13.712%	$243.8326	$243.83	$243.85	$243.80
Purchase #4	$165.66	7.573%	$178.2054	$178.21	$178.20	$178.20
Purchase #5	$38.43	4.736%	$40.25	$40.25	$40.25	$40.30
Purchase #6	$139.93	11.408%	$155.8932	$155.89	$155.90	$155.90
Purchase #7	$70.49	13.589%	$80.0689	$80.07	$80.05	$80.10
7 purchase totals =	$654.59		$724.8811	$724.88	$724.90	$724.90