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	$216.46	3.119%	$223.2114	$223.21	$223.20	$223.20
Purchase #2	$94.85	4.839%	$99.4398	$99.44	$99.45	$99.40
Purchase #3	$125.45	13.384%	$142.2402	$142.24	$142.25	$142.20
Purchase #4	$226.88	12.768%	$255.848	$255.85	$255.85	$255.80
Purchase #5	$40.89	6.730%	$43.6419	$43.64	$43.65	$43.60
Purchase #6	$62.38	6.179%	$66.2345	$66.23	$66.25	$66.20
Purchase #7	$149.91	7.595%	$161.2957	$161.30	$161.30	$161.30
7 purchase totals =	$916.82		$991.9115	$991.91	$991.95	$991.70