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	$54.39	9.838%	$59.7409	$59.74	$59.75	$59.70
Purchase #2	$65.82	3.133%	$67.8821	$67.88	$67.90	$67.90
Purchase #3	$132.75	13.558%	$150.7482	$150.75	$150.75	$150.70
Purchase #4	$115.37	6.733%	$123.1379	$123.14	$123.15	$123.10
Purchase #5	$246.91	11.297%	$274.8034	$274.80	$274.80	$274.80
Purchase #6	$143.31	8.307%	$155.2148	$155.21	$155.20	$155.20
Purchase #7	$10.52	11.111%	$11.6889	$11.69	$11.70	$11.70
7 purchase totals =	$769.07		$843.2162	$843.21	$843.25	$843.10