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	$36.51	4.807%	$38.265	$38.27	$38.25	$38.30
Purchase #2	$90.29	12.462%	$101.5419	$101.54	$101.55	$101.50
Purchase #3	$78.37	12.566%	$88.218	$88.22	$88.20	$88.20
Purchase #4	$55.71	5.608%	$58.8342	$58.83	$58.85	$58.80
Purchase #5	$66.61	9.238%	$72.7634	$72.76	$72.75	$72.80
Purchase #6	$151.43	6.546%	$161.3426	$161.34	$161.35	$161.30
Purchase #7	$92.66	10.601%	$102.4829	$102.48	$102.50	$102.50
7 purchase totals =	$571.58		$623.4480	$623.44	$623.45	$623.40