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	$113.48	11.572%	$126.6119	$126.61	$126.60	$126.60
Purchase #2	$227.32	13.177%	$257.274	$257.27	$257.25	$257.30
Purchase #3	$65.65	8.578%	$71.2815	$71.28	$71.30	$71.30
Purchase #4	$41.59	4.455%	$43.4428	$43.44	$43.45	$43.40
Purchase #5	$237.94	7.861%	$256.6445	$256.64	$256.65	$256.60
Purchase #6	$145.71	9.497%	$159.5481	$159.55	$159.55	$159.50
Purchase #7	$76.59	10.736%	$84.8127	$84.81	$84.80	$84.80
7 purchase totals =	$908.28		$999.6155	$999.60	$999.60	$999.50