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	$247.89	3.609%	$256.8364	$256.84	$256.85	$256.80
Purchase #2	$30.57	5.729%	$32.3214	$32.32	$32.30	$32.30
Purchase #3	$57.32	11.867%	$64.1222	$64.12	$64.10	$64.10
Purchase #4	$237.67	7.659%	$255.8731	$255.87	$255.85	$255.90
Purchase #5	$46.60	5.303%	$49.0712	$49.07	$49.05	$49.10
Purchase #6	$234.80	12.769%	$264.7816	$264.78	$264.80	$264.80
Purchase #7	$68.28	6.375%	$72.6329	$72.63	$72.65	$72.60
7 purchase totals =	$923.13		$995.6388	$995.63	$995.60	$995.60