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	$127.77	11.323%	$142.2374	$142.24	$142.25	$142.20
Purchase #2	$44.31	11.214%	$49.2789	$49.28	$49.30	$49.30
Purchase #3	$201.31	8.327%	$218.0731	$218.07	$218.05	$218.10
Purchase #4	$167.35	11.406%	$186.4379	$186.44	$186.45	$186.40
Purchase #5	$99.80	9.721%	$109.5016	$109.50	$109.50	$109.50
Purchase #6	$34.37	11.720%	$38.3982	$38.40	$38.40	$38.40
Purchase #7	$50.79	3.546%	$52.591	$52.59	$52.60	$52.60
7 purchase totals =	$725.70		$796.5181	$796.52	$796.55	$796.50