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	$24.39	12.620%	$27.468	$27.47	$27.45	$27.50
Purchase #2	$122.41	5.554%	$129.2087	$129.21	$129.20	$129.20
Purchase #3	$114.25	4.367%	$119.2393	$119.24	$119.25	$119.20
Purchase #4	$176.61	13.466%	$200.3923	$200.39	$200.40	$200.40
Purchase #5	$226.44	5.144%	$238.0881	$238.09	$238.10	$238.10
Purchase #6	$230.56	13.567%	$261.8401	$261.84	$261.85	$261.80
Purchase #7	$35.81	13.677%	$40.7077	$40.71	$40.70	$40.70
7 purchase totals =	$930.47		$1,016.9442	$1,016.95	$1,016.95	$1,016.90