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	$21.45	12.573%	$24.1469	$24.15	$24.15	$24.10
Purchase #2	$154.70	7.226%	$165.8786	$165.88	$165.90	$165.90
Purchase #3	$38.64	10.397%	$42.6574	$42.66	$42.65	$42.70
Purchase #4	$242.98	10.693%	$268.9619	$268.96	$268.95	$269.00
Purchase #5	$25.83	13.120%	$29.2189	$29.22	$29.20	$29.20
Purchase #6	$52.62	13.699%	$59.8284	$59.83	$59.85	$59.80
Purchase #7	$29.25	7.412%	$31.418	$31.42	$31.40	$31.40
7 purchase totals =	$565.47		$622.1101	$622.12	$622.10	$622.10