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	$9.89	9.277%	$10.8075	$10.81	$10.80	$10.80
Purchase #2	$40.57	8.201%	$43.8971	$43.90	$43.90	$43.90
Purchase #3	$99.25	12.739%	$111.8935	$111.89	$111.90	$111.90
Purchase #4	$225.90	9.743%	$247.9094	$247.91	$247.90	$247.90
Purchase #5	$245.60	13.128%	$277.8424	$277.84	$277.85	$277.80
Purchase #6	$179.46	11.580%	$200.2415	$200.24	$200.25	$200.20
Purchase #7	$205.40	4.465%	$214.5711	$214.57	$214.55	$214.60
7 purchase totals =	$1,006.07		$1,107.1625	$1,107.16	$1,107.15	$1,107.10