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	$240.59	11.760%	$268.8834	$268.88	$268.90	$268.90
Purchase #2	$87.91	4.194%	$91.5969	$91.60	$91.60	$91.60
Purchase #3	$60.63	9.105%	$66.1504	$66.15	$66.15	$66.20
Purchase #4	$97.45	12.416%	$109.5494	$109.55	$109.55	$109.50
Purchase #5	$123.50	5.627%	$130.4493	$130.45	$130.45	$130.40
Purchase #6	$173.60	4.798%	$181.9293	$181.93	$181.95	$181.90
Purchase #7	$108.27	11.289%	$120.4926	$120.49	$120.50	$120.50
7 purchase totals =	$891.95		$969.0513	$969.05	$969.10	$969.00