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	$57.98	10.701%	$64.1844	$64.18	$64.20	$64.20
Purchase #2	$156.70	13.333%	$177.5928	$177.59	$177.60	$177.60
Purchase #3	$38.34	8.615%	$41.643	$41.64	$41.65	$41.60
Purchase #4	$97.34	3.198%	$100.4529	$100.45	$100.45	$100.50
Purchase #5	$47.89	8.743%	$52.077	$52.08	$52.10	$52.10
Purchase #6	$59.54	10.642%	$65.8762	$65.88	$65.90	$65.90
Purchase #7	$127.26	9.496%	$139.3446	$139.34	$139.35	$139.30
7 purchase totals =	$585.05		$641.1709	$641.16	$641.25	$641.20