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	$186.87	10.491%	$206.4745	$206.47	$206.45	$206.50
Purchase #2	$53.43	11.490%	$59.5691	$59.57	$59.55	$59.60
Purchase #3	$17.66	3.640%	$18.3028	$18.30	$18.30	$18.30
Purchase #4	$18.83	6.446%	$20.0438	$20.04	$20.05	$20.00
Purchase #5	$68.92	5.174%	$72.4859	$72.49	$72.50	$72.50
Purchase #6	$29.45	7.454%	$31.6452	$31.65	$31.65	$31.60
Purchase #7	$107.76	6.215%	$114.4573	$114.46	$114.45	$114.50
7 purchase totals =	$482.92		$522.9786	$522.98	$522.95	$523.00