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	$47.37	12.272%	$53.1832	$53.18	$53.20	$53.20
Purchase #2	$34.45	13.686%	$39.1648	$39.16	$39.15	$39.20
Purchase #3	$72.25	10.866%	$80.1007	$80.10	$80.10	$80.10
Purchase #4	$59.36	8.142%	$64.1931	$64.19	$64.20	$64.20
Purchase #5	$196.54	6.266%	$208.8552	$208.86	$208.85	$208.90
Purchase #6	$13.97	9.333%	$15.2738	$15.27	$15.25	$15.30
Purchase #7	$43.98	3.664%	$45.5914	$45.59	$45.60	$45.60
7 purchase totals =	$467.92		$506.3622	$506.35	$506.35	$506.50