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	$76.93	13.530%	$87.3386	$87.34	$87.35	$87.30
Purchase #2	$170.61	8.524%	$185.1528	$185.15	$185.15	$185.20
Purchase #3	$127.88	12.580%	$143.9673	$143.97	$143.95	$144.00
Purchase #4	$196.55	12.755%	$221.62	$221.62	$221.60	$221.60
Purchase #5	$19.35	5.603%	$20.4342	$20.43	$20.45	$20.40
Purchase #6	$88.86	12.831%	$100.2616	$100.26	$100.25	$100.30
Purchase #7	$151.27	5.564%	$159.6867	$159.69	$159.70	$159.70
7 purchase totals =	$831.45		$918.4612	$918.46	$918.45	$918.50