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	$133.78	7.774%	$144.1801	$144.18	$144.20	$144.20
Purchase #2	$138.63	3.655%	$143.6969	$143.70	$143.70	$143.70
Purchase #3	$168.42	5.287%	$177.3244	$177.32	$177.30	$177.30
Purchase #4	$111.52	11.141%	$123.9444	$123.94	$123.95	$123.90
Purchase #5	$164.69	12.606%	$185.4508	$185.45	$185.45	$185.50
Purchase #6	$23.78	6.130%	$25.2377	$25.24	$25.25	$25.20
Purchase #7	$144.28	7.808%	$155.5454	$155.55	$155.55	$155.50
7 purchase totals =	$885.10		$955.3797	$955.38	$955.40	$955.30