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	$179.83	10.388%	$198.5107	$198.51	$198.50	$198.50
Purchase #2	$85.97	3.858%	$89.2867	$89.29	$89.30	$89.30
Purchase #3	$17.90	5.395%	$18.8657	$18.87	$18.85	$18.90
Purchase #4	$237.88	9.286%	$259.9695	$259.97	$259.95	$260.00
Purchase #5	$102.28	6.476%	$108.9037	$108.90	$108.90	$108.90
Purchase #6	$57.34	13.755%	$65.2271	$65.23	$65.25	$65.20
Purchase #7	$245.84	5.713%	$259.8848	$259.88	$259.90	$259.90
7 purchase totals =	$927.04		$1,000.6482	$1,000.65	$1,000.65	$1,000.70