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	$14.70	5.575%	$15.5195	$15.52	$15.50	$15.50
Purchase #2	$124.86	11.566%	$139.3013	$139.30	$139.30	$139.30
Purchase #3	$128.74	13.781%	$146.4817	$146.48	$146.50	$146.50
Purchase #4	$127.89	9.870%	$140.5127	$140.51	$140.50	$140.50
Purchase #5	$9.36	6.792%	$9.9957	$10.00	$10.00	$10.00
Purchase #6	$208.50	6.409%	$221.8628	$221.86	$221.85	$221.90
Purchase #7	$29.83	6.189%	$31.6762	$31.68	$31.70	$31.70
7 purchase totals =	$643.88		$705.3499	$705.35	$705.35	$705.40