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	$82.93	7.428%	$89.09	$89.09	$89.10	$89.10
Purchase #2	$48.83	4.545%	$51.0493	$51.05	$51.05	$51.00
Purchase #3	$51.39	10.245%	$56.6549	$56.65	$56.65	$56.70
Purchase #4	$95.51	8.138%	$103.2826	$103.28	$103.30	$103.30
Purchase #5	$66.35	10.353%	$73.2192	$73.22	$73.20	$73.20
Purchase #6	$234.34	8.817%	$255.0018	$255.00	$255.00	$255.00
Purchase #7	$128.72	12.556%	$144.8821	$144.88	$144.90	$144.90
7 purchase totals =	$708.07		$773.1799	$773.17	$773.20	$773.20