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	$30.31	4.686%	$31.7303	$31.73	$31.75	$31.70
Purchase #2	$29.28	11.431%	$32.627	$32.63	$32.65	$32.60
Purchase #3	$52.66	12.497%	$59.2409	$59.24	$59.25	$59.20
Purchase #4	$224.92	12.471%	$252.9698	$252.97	$252.95	$253.00
Purchase #5	$91.64	9.593%	$100.431	$100.43	$100.45	$100.40
Purchase #6	$64.32	5.493%	$67.8531	$67.85	$67.85	$67.90
Purchase #7	$51.51	6.393%	$54.803	$54.80	$54.80	$54.80
7 purchase totals =	$544.64		$599.6551	$599.65	$599.70	$599.60