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	$39.43	8.769%	$42.8876	$42.89	$42.90	$42.90
Purchase #2	$36.32	11.809%	$40.609	$40.61	$40.60	$40.60
Purchase #3	$172.51	12.853%	$194.6827	$194.68	$194.70	$194.70
Purchase #4	$141.61	10.282%	$156.1703	$156.17	$156.15	$156.20
Purchase #5	$49.46	9.357%	$54.088	$54.09	$54.10	$54.10
Purchase #6	$184.78	4.489%	$193.0748	$193.07	$193.05	$193.10
Purchase #7	$120.51	5.459%	$127.0886	$127.09	$127.10	$127.10
7 purchase totals =	$744.62		$808.6010	$808.60	$808.60	$808.70