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	$36.98	12.339%	$41.543	$41.54	$41.55	$41.50
Purchase #2	$214.56	12.855%	$242.1417	$242.14	$242.15	$242.10
Purchase #3	$213.53	10.834%	$236.6638	$236.66	$236.65	$236.70
Purchase #4	$226.27	7.592%	$243.4484	$243.45	$243.45	$243.40
Purchase #5	$84.85	6.176%	$90.0903	$90.09	$90.10	$90.10
Purchase #6	$128.47	10.159%	$141.5213	$141.52	$141.50	$141.50
Purchase #7	$102.36	5.795%	$108.2918	$108.29	$108.30	$108.30
7 purchase totals =	$1,007.02		$1,103.7003	$1,103.69	$1,103.70	$1,103.60