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	$117.37	12.702%	$132.2783	$132.28	$132.30	$132.30
Purchase #2	$37.67	8.415%	$40.8399	$40.84	$40.85	$40.80
Purchase #3	$155.94	11.763%	$174.2832	$174.28	$174.30	$174.30
Purchase #4	$34.34	6.683%	$36.6349	$36.63	$36.65	$36.60
Purchase #5	$99.91	12.379%	$112.2779	$112.28	$112.30	$112.30
Purchase #6	$47.76	13.141%	$54.0361	$54.04	$54.05	$54.00
Purchase #7	$108.89	6.388%	$115.8459	$115.85	$115.85	$115.80
7 purchase totals =	$601.88		$666.1962	$666.20	$666.30	$666.10