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	$134.65	3.564%	$139.4489	$139.45	$139.45	$139.40
Purchase #2	$231.43	9.770%	$254.0407	$254.04	$254.05	$254.00
Purchase #3	$133.56	7.871%	$144.0725	$144.07	$144.05	$144.10
Purchase #4	$124.36	10.561%	$137.4937	$137.49	$137.50	$137.50
Purchase #5	$49.33	13.169%	$55.8263	$55.83	$55.85	$55.80
Purchase #6	$130.56	8.378%	$141.4983	$141.50	$141.50	$141.50
Purchase #7	$207.28	9.825%	$227.6453	$227.65	$227.65	$227.60
7 purchase totals =	$1,011.17		$1,100.0257	$1,100.03	$1,100.05	$1,099.90