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	$39.40	11.365%	$43.8778	$43.88	$43.90	$43.90
Purchase #2	$130.80	6.339%	$139.0914	$139.09	$139.10	$139.10
Purchase #3	$11.72	5.121%	$12.3202	$12.32	$12.30	$12.30
Purchase #4	$137.26	11.734%	$153.3661	$153.37	$153.35	$153.40
Purchase #5	$22.56	10.440%	$24.9153	$24.92	$24.90	$24.90
Purchase #6	$75.72	12.365%	$85.0828	$85.08	$85.10	$85.10
Purchase #7	$25.79	12.268%	$28.9539	$28.95	$28.95	$29.00
7 purchase totals =	$443.25		$487.6075	$487.61	$487.60	$487.70