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	$229.76	12.651%	$258.8269	$258.83	$258.85	$258.80
Purchase #2	$151.87	13.186%	$171.8956	$171.90	$171.90	$171.90
Purchase #3	$166.47	8.395%	$180.4452	$180.45	$180.45	$180.40
Purchase #4	$74.75	7.188%	$80.123	$80.12	$80.10	$80.10
Purchase #5	$116.34	12.114%	$130.4334	$130.43	$130.45	$130.40
Purchase #6	$154.37	6.839%	$164.9274	$164.93	$164.95	$164.90
Purchase #7	$127.78	4.421%	$133.4292	$133.43	$133.45	$133.40
7 purchase totals =	$1,021.34		$1,120.0807	$1,120.09	$1,120.15	$1,119.90