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	$24.48	5.834%	$25.9082	$25.91	$25.90	$25.90
Purchase #2	$82.71	11.757%	$92.4342	$92.43	$92.45	$92.40
Purchase #3	$203.95	12.572%	$229.5906	$229.59	$229.60	$229.60
Purchase #4	$13.32	4.154%	$13.8733	$13.87	$13.85	$13.90
Purchase #5	$169.53	8.829%	$184.4978	$184.50	$184.50	$184.50
Purchase #6	$76.62	11.594%	$85.5033	$85.50	$85.50	$85.50
Purchase #7	$45.59	5.871%	$48.2666	$48.27	$48.25	$48.30
7 purchase totals =	$616.20		$680.0740	$680.07	$680.05	$680.10