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	$152.42	11.831%	$170.4528	$170.45	$170.45	$170.50
Purchase #2	$116.82	5.583%	$123.3421	$123.34	$123.35	$123.30
Purchase #3	$219.62	7.683%	$236.4934	$236.49	$236.50	$236.50
Purchase #4	$81.36	12.381%	$91.4332	$91.43	$91.45	$91.40
Purchase #5	$241.83	5.718%	$255.6578	$255.66	$255.65	$255.70
Purchase #6	$211.67	13.226%	$239.6655	$239.67	$239.65	$239.70
Purchase #7	$181.31	5.658%	$191.5685	$191.57	$191.55	$191.60
7 purchase totals =	$1,205.03		$1,308.6133	$1,308.61	$1,308.60	$1,308.70