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	$160.26	6.424%	$170.5551	$170.56	$170.55	$170.60
Purchase #2	$228.45	13.229%	$258.6717	$258.67	$258.65	$258.70
Purchase #3	$153.41	4.207%	$159.864	$159.86	$159.85	$159.90
Purchase #4	$223.48	4.810%	$234.2294	$234.23	$234.25	$234.20
Purchase #5	$139.56	5.845%	$147.7173	$147.72	$147.70	$147.70
Purchase #6	$167.78	5.139%	$176.4022	$176.40	$176.40	$176.40
Purchase #7	$113.56	12.240%	$127.4597	$127.46	$127.45	$127.50
7 purchase totals =	$1,186.50		$1,274.8994	$1,274.90	$1,274.85	$1,275.00