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	$224.47	13.831%	$255.5164	$255.52	$255.50	$255.50
Purchase #2	$188.27	13.303%	$213.3156	$213.32	$213.30	$213.30
Purchase #3	$157.35	13.472%	$178.5482	$178.55	$178.55	$178.50
Purchase #4	$36.68	8.419%	$39.7681	$39.77	$39.75	$39.80
Purchase #5	$83.32	13.478%	$94.5499	$94.55	$94.55	$94.50
Purchase #6	$37.30	12.323%	$41.8965	$41.90	$41.90	$41.90
Purchase #7	$247.90	12.663%	$279.2916	$279.29	$279.30	$279.30
7 purchase totals =	$975.29		$1,102.8863	$1,102.90	$1,102.85	$1,102.80