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	$48.45	12.526%	$54.5188	$54.52	$54.50	$54.50
Purchase #2	$47.59	11.591%	$53.1062	$53.11	$53.10	$53.10
Purchase #3	$92.84	9.370%	$101.5391	$101.54	$101.55	$101.50
Purchase #4	$49.28	8.723%	$53.5787	$53.58	$53.60	$53.60
Purchase #5	$53.45	9.596%	$58.5791	$58.58	$58.60	$58.60
Purchase #6	$150.51	11.440%	$167.7283	$167.73	$167.75	$167.70
Purchase #7	$145.87	11.274%	$162.3154	$162.32	$162.30	$162.30
7 purchase totals =	$587.99		$651.3656	$651.38	$651.40	$651.30