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	$81.34	4.623%	$85.1003	$85.10	$85.10	$85.10
Purchase #2	$197.51	8.847%	$214.9837	$214.98	$215.00	$215.00
Purchase #3	$65.87	9.433%	$72.0835	$72.08	$72.10	$72.10
Purchase #4	$122.32	13.756%	$139.1463	$139.15	$139.15	$139.10
Purchase #5	$70.54	4.756%	$73.8949	$73.89	$73.90	$73.90
Purchase #6	$57.89	7.765%	$62.3852	$62.39	$62.40	$62.40
Purchase #7	$158.54	12.785%	$178.8093	$178.81	$178.80	$178.80
7 purchase totals =	$754.01		$826.4032	$826.40	$826.45	$826.40