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	$246.28	13.691%	$279.9982	$280.00	$280.00	$280.00
Purchase #2	$133.92	11.381%	$149.1614	$149.16	$149.15	$149.20
Purchase #3	$75.75	9.372%	$82.8493	$82.85	$82.85	$82.80
Purchase #4	$45.65	7.829%	$49.2239	$49.22	$49.20	$49.20
Purchase #5	$150.80	5.714%	$159.4167	$159.42	$159.40	$159.40
Purchase #6	$73.70	6.300%	$78.3431	$78.34	$78.35	$78.30
Purchase #7	$195.81	12.576%	$220.4351	$220.44	$220.45	$220.40
7 purchase totals =	$921.91		$1,019.4277	$1,019.43	$1,019.40	$1,019.30