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	$53.63	11.597%	$59.8495	$59.85	$59.85	$59.80
Purchase #2	$41.49	9.658%	$45.4971	$45.50	$45.50	$45.50
Purchase #3	$100.44	13.841%	$114.3419	$114.34	$114.35	$114.30
Purchase #4	$48.51	8.170%	$52.4733	$52.47	$52.45	$52.50
Purchase #5	$7.69	7.444%	$8.2624	$8.26	$8.25	$8.30
Purchase #6	$126.66	5.468%	$133.5858	$133.59	$133.60	$133.60
Purchase #7	$174.26	7.410%	$187.1727	$187.17	$187.15	$187.20
7 purchase totals =	$552.68		$601.1827	$601.18	$601.15	$601.20