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	$53.93	4.374%	$56.2889	$56.29	$56.30	$56.30
Purchase #2	$125.72	8.375%	$136.2491	$136.25	$136.25	$136.20
Purchase #3	$175.43	5.251%	$184.6418	$184.64	$184.65	$184.60
Purchase #4	$145.90	7.270%	$156.5069	$156.51	$156.50	$156.50
Purchase #5	$46.45	4.416%	$48.5012	$48.50	$48.50	$48.50
Purchase #6	$64.82	12.353%	$72.8272	$72.83	$72.85	$72.80
Purchase #7	$243.88	9.305%	$266.573	$266.57	$266.55	$266.60
7 purchase totals =	$856.13		$921.5881	$921.59	$921.60	$921.50