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	$249.94	5.863%	$264.594	$264.59	$264.60	$264.60
Purchase #2	$140.47	6.852%	$150.095	$150.10	$150.10	$150.10
Purchase #3	$29.54	4.106%	$30.7529	$30.75	$30.75	$30.80
Purchase #4	$232.74	9.786%	$255.5159	$255.52	$255.50	$255.50
Purchase #5	$245.93	10.128%	$270.8378	$270.84	$270.85	$270.80
Purchase #6	$203.65	12.265%	$228.6277	$228.63	$228.65	$228.60
Purchase #7	$54.79	8.798%	$59.6104	$59.61	$59.60	$59.60
7 purchase totals =	$1,157.06		$1,260.0337	$1,260.04	$1,260.05	$1,260.00