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	$30.98	12.662%	$34.9027	$34.90	$34.90	$34.90
Purchase #2	$167.75	10.388%	$185.1759	$185.18	$185.20	$185.20
Purchase #3	$52.96	6.105%	$56.1932	$56.19	$56.20	$56.20
Purchase #4	$139.98	11.843%	$156.5578	$156.56	$156.55	$156.60
Purchase #5	$127.73	9.466%	$139.8209	$139.82	$139.80	$139.80
Purchase #6	$78.45	5.507%	$82.7702	$82.77	$82.75	$82.80
Purchase #7	$223.86	8.433%	$242.7381	$242.74	$242.75	$242.70
7 purchase totals =	$821.71		$898.1588	$898.16	$898.15	$898.20