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	$51.71	11.418%	$57.6142	$57.61	$57.60	$57.60
Purchase #2	$27.71	5.686%	$29.2856	$29.29	$29.30	$29.30
Purchase #3	$55.57	13.591%	$63.1225	$63.12	$63.10	$63.10
Purchase #4	$86.76	4.173%	$90.3805	$90.38	$90.40	$90.40
Purchase #5	$236.40	11.421%	$263.3992	$263.40	$263.40	$263.40
Purchase #6	$49.53	9.874%	$54.4206	$54.42	$54.40	$54.40
Purchase #7	$32.99	4.808%	$34.5762	$34.58	$34.60	$34.60
7 purchase totals =	$540.67		$592.7988	$592.80	$592.80	$592.80