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	$10.93	9.228%	$11.9386	$11.94	$11.95	$11.90
Purchase #2	$149.62	8.553%	$162.417	$162.42	$162.40	$162.40
Purchase #3	$87.91	8.758%	$95.6092	$95.61	$95.60	$95.60
Purchase #4	$71.94	9.559%	$78.8167	$78.82	$78.80	$78.80
Purchase #5	$201.28	6.791%	$214.9489	$214.95	$214.95	$214.90
Purchase #6	$87.54	12.464%	$98.451	$98.45	$98.45	$98.50
Purchase #7	$139.86	11.778%	$156.3327	$156.33	$156.35	$156.30
7 purchase totals =	$749.08		$818.5141	$818.52	$818.50	$818.40