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	$156.28	6.700%	$166.7508	$166.75	$166.75	$166.80
Purchase #2	$118.55	7.743%	$127.7293	$127.73	$127.75	$127.70
Purchase #3	$160.30	4.688%	$167.8149	$167.81	$167.80	$167.80
Purchase #4	$18.52	13.536%	$21.0269	$21.03	$21.05	$21.00
Purchase #5	$63.95	11.571%	$71.3497	$71.35	$71.35	$71.30
Purchase #6	$123.56	12.819%	$139.3992	$139.40	$139.40	$139.40
Purchase #7	$235.38	3.824%	$244.3809	$244.38	$244.40	$244.40
7 purchase totals =	$876.54		$938.4517	$938.45	$938.50	$938.40