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	$12.52	13.107%	$14.161	$14.16	$14.15	$14.20
Purchase #2	$140.45	13.839%	$159.8869	$159.89	$159.90	$159.90
Purchase #3	$164.74	3.438%	$170.4038	$170.40	$170.40	$170.40
Purchase #4	$48.43	13.196%	$54.8208	$54.82	$54.80	$54.80
Purchase #5	$123.38	3.447%	$127.6329	$127.63	$127.65	$127.60
Purchase #6	$64.89	12.408%	$72.9416	$72.94	$72.95	$72.90
Purchase #7	$31.82	13.760%	$36.1984	$36.20	$36.20	$36.20
7 purchase totals =	$586.23		$636.0454	$636.04	$636.05	$636.00