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	$60.82	9.353%	$66.5085	$66.51	$66.50	$66.50
Purchase #2	$144.93	9.749%	$159.0592	$159.06	$159.05	$159.10
Purchase #3	$139.87	7.110%	$149.8148	$149.81	$149.80	$149.80
Purchase #4	$38.38	11.296%	$42.7154	$42.72	$42.70	$42.70
Purchase #5	$187.39	4.661%	$196.1242	$196.12	$196.10	$196.10
Purchase #6	$154.89	12.514%	$174.2729	$174.27	$174.25	$174.30
Purchase #7	$71.28	8.765%	$77.5277	$77.53	$77.55	$77.50
7 purchase totals =	$797.56		$866.0227	$866.02	$865.95	$866.00