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	$171.64	7.123%	$183.8659	$183.87	$183.85	$183.90
Purchase #2	$34.69	9.304%	$37.9176	$37.92	$37.90	$37.90
Purchase #3	$107.94	10.152%	$118.8981	$118.90	$118.90	$118.90
Purchase #4	$127.88	4.174%	$133.2177	$133.22	$133.20	$133.20
Purchase #5	$105.98	6.551%	$112.9227	$112.92	$112.90	$112.90
Purchase #6	$200.48	8.465%	$217.4506	$217.45	$217.45	$217.50
Purchase #7	$38.93	5.106%	$40.9178	$40.92	$40.90	$40.90
7 purchase totals =	$787.54		$845.1904	$845.20	$845.10	$845.20