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	$126.85	6.484%	$135.075	$135.08	$135.10	$135.10
Purchase #2	$74.79	8.103%	$80.8502	$80.85	$80.85	$80.90
Purchase #3	$103.89	8.634%	$112.8599	$112.86	$112.85	$112.90
Purchase #4	$100.50	10.598%	$111.151	$111.15	$111.15	$111.20
Purchase #5	$21.52	11.624%	$24.0215	$24.02	$24.00	$24.00
Purchase #6	$250.66	11.640%	$279.8368	$279.84	$279.85	$279.80
Purchase #7	$118.37	8.326%	$128.2255	$128.23	$128.25	$128.20
7 purchase totals =	$796.58		$872.0199	$872.03	$872.05	$872.10