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	$120.83	5.195%	$127.1071	$127.11	$127.10	$127.10
Purchase #2	$228.92	7.384%	$245.8235	$245.82	$245.80	$245.80
Purchase #3	$129.73	5.734%	$137.1687	$137.17	$137.15	$137.20
Purchase #4	$114.39	11.500%	$127.5449	$127.54	$127.55	$127.50
Purchase #5	$143.38	11.569%	$159.9676	$159.97	$159.95	$160.00
Purchase #6	$193.65	12.234%	$217.3411	$217.34	$217.35	$217.30
Purchase #7	$139.88	13.417%	$158.6477	$158.65	$158.65	$158.60
7 purchase totals =	$1,070.78		$1,173.6006	$1,173.60	$1,173.55	$1,173.50