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	$50.83	12.752%	$57.3118	$57.31	$57.30	$57.30
Purchase #2	$112.35	13.591%	$127.6195	$127.62	$127.60	$127.60
Purchase #3	$172.56	7.756%	$185.9438	$185.94	$185.95	$185.90
Purchase #4	$230.45	13.476%	$261.5054	$261.51	$261.50	$261.50
Purchase #5	$162.54	3.562%	$168.3297	$168.33	$168.35	$168.30
Purchase #6	$12.65	10.325%	$13.9561	$13.96	$13.95	$14.00
Purchase #7	$39.52	3.497%	$40.902	$40.90	$40.90	$40.90
7 purchase totals =	$780.90		$855.5683	$855.57	$855.55	$855.50