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	$138.31	10.337%	$152.6071	$152.61	$152.60	$152.60
Purchase #2	$103.91	9.575%	$113.8594	$113.86	$113.85	$113.90
Purchase #3	$136.51	7.743%	$147.08	$147.08	$147.10	$147.10
Purchase #4	$238.27	7.610%	$256.4023	$256.40	$256.40	$256.40
Purchase #5	$76.45	13.579%	$86.8311	$86.83	$86.85	$86.80
Purchase #6	$207.73	7.545%	$223.4032	$223.40	$223.40	$223.40
Purchase #7	$158.59	7.839%	$171.0219	$171.02	$171.00	$171.00
7 purchase totals =	$1,059.77		$1,151.2050	$1,151.20	$1,151.20	$1,151.20