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	$159.30	6.150%	$169.097	$169.10	$169.10	$169.10
Purchase #2	$107.56	6.564%	$114.6202	$114.62	$114.60	$114.60
Purchase #3	$189.31	3.766%	$196.4394	$196.44	$196.45	$196.40
Purchase #4	$13.49	13.311%	$15.2857	$15.29	$15.30	$15.30
Purchase #5	$164.82	9.863%	$181.0762	$181.08	$181.10	$181.10
Purchase #6	$32.85	11.486%	$36.6232	$36.62	$36.60	$36.60
Purchase #7	$37.42	8.170%	$40.4772	$40.48	$40.50	$40.50
7 purchase totals =	$704.75		$753.6189	$753.63	$753.65	$753.60