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	13.798%	$59.7781	$59.78	$59.80	$59.80
Purchase #2	$176.68	10.845%	$195.8409	$195.84	$195.85	$195.80
Purchase #3	$80.91	6.188%	$85.9167	$85.92	$85.90	$85.90
Purchase #4	$185.39	8.870%	$201.8341	$201.83	$201.85	$201.80
Purchase #5	$118.68	3.769%	$123.153	$123.15	$123.15	$123.20
Purchase #6	$105.41	3.253%	$108.839	$108.84	$108.85	$108.80
Purchase #7	$188.50	5.832%	$199.4933	$199.49	$199.50	$199.50
7 purchase totals =	$908.10		$974.8551	$974.85	$974.90	$974.80