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	$52.53	7.644%	$56.5454	$56.55	$56.55	$56.50
Purchase #2	$95.76	8.464%	$103.8651	$103.87	$103.85	$103.90
Purchase #3	$166.43	12.697%	$187.5616	$187.56	$187.55	$187.60
Purchase #4	$84.77	3.477%	$87.7175	$87.72	$87.70	$87.70
Purchase #5	$144.41	4.144%	$150.3944	$150.39	$150.40	$150.40
Purchase #6	$27.31	7.399%	$29.3307	$29.33	$29.35	$29.30
Purchase #7	$173.58	9.733%	$190.4745	$190.47	$190.45	$190.50
7 purchase totals =	$744.79		$805.8892	$805.89	$805.85	$805.90