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	$181.40	3.205%	$187.2139	$187.21	$187.20	$187.20
Purchase #2	$250.67	4.246%	$261.3134	$261.31	$261.30	$261.30
Purchase #3	$95.95	7.181%	$102.8402	$102.84	$102.85	$102.80
Purchase #4	$179.93	9.386%	$196.8182	$196.82	$196.80	$196.80
Purchase #5	$37.56	5.553%	$39.6457	$39.65	$39.65	$39.60
Purchase #6	$58.55	4.605%	$61.2462	$61.25	$61.25	$61.20
Purchase #7	$56.95	4.297%	$59.3971	$59.40	$59.40	$59.40
7 purchase totals =	$861.01		$908.4747	$908.48	$908.45	$908.30