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	$137.49	12.540%	$154.7312	$154.73	$154.75	$154.70
Purchase #2	$176.63	5.246%	$185.896	$185.90	$185.90	$185.90
Purchase #3	$155.70	8.295%	$168.6153	$168.62	$168.60	$168.60
Purchase #4	$37.51	12.704%	$42.2753	$42.28	$42.30	$42.30
Purchase #5	$139.95	9.106%	$152.6938	$152.69	$152.70	$152.70
Purchase #6	$96.94	6.297%	$103.0443	$103.04	$103.05	$103.00
Purchase #7	$178.84	5.741%	$189.1072	$189.11	$189.10	$189.10
7 purchase totals =	$923.06		$996.3631	$996.37	$996.40	$996.30