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	$134.94	12.347%	$151.601	$151.60	$151.60	$151.60
Purchase #2	$115.75	3.104%	$119.3429	$119.34	$119.35	$119.30
Purchase #3	$96.41	11.136%	$107.1462	$107.15	$107.15	$107.10
Purchase #4	$168.35	4.184%	$175.3938	$175.39	$175.40	$175.40
Purchase #5	$29.35	13.194%	$33.2224	$33.22	$33.20	$33.20
Purchase #6	$154.40	11.177%	$171.6573	$171.66	$171.65	$171.70
Purchase #7	$65.51	11.262%	$72.8877	$72.89	$72.90	$72.90
7 purchase totals =	$764.71		$831.2513	$831.25	$831.25	$831.20