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	$9.25	9.268%	$10.1073	$10.11	$10.10	$10.10
Purchase #2	$64.99	12.192%	$72.9136	$72.91	$72.90	$72.90
Purchase #3	$24.85	8.360%	$26.9275	$26.93	$26.95	$26.90
Purchase #4	$230.51	13.451%	$261.5159	$261.52	$261.50	$261.50
Purchase #5	$139.80	7.495%	$150.278	$150.28	$150.30	$150.30
Purchase #6	$51.80	5.748%	$54.7775	$54.78	$54.80	$54.80
Purchase #7	$88.73	13.613%	$100.8088	$100.81	$100.80	$100.80
7 purchase totals =	$609.93		$677.3286	$677.34	$677.35	$677.30