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	$171.84	4.132%	$178.9404	$178.94	$178.95	$178.90
Purchase #2	$122.33	9.652%	$134.1373	$134.14	$134.15	$134.10
Purchase #3	$42.40	10.486%	$46.8461	$46.85	$46.85	$46.80
Purchase #4	$29.25	10.274%	$32.2551	$32.26	$32.25	$32.30
Purchase #5	$185.62	3.189%	$191.5394	$191.54	$191.55	$191.50
Purchase #6	$116.88	9.863%	$128.4079	$128.41	$128.40	$128.40
Purchase #7	$47.86	12.854%	$54.0119	$54.01	$54.00	$54.00
7 purchase totals =	$716.18		$766.1381	$766.15	$766.15	$766.00