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	$138.42	4.246%	$144.2973	$144.30	$144.30	$144.30
Purchase #2	$53.69	7.184%	$57.5471	$57.55	$57.55	$57.50
Purchase #3	$165.48	12.385%	$185.9747	$185.97	$185.95	$186.00
Purchase #4	$157.47	9.384%	$172.247	$172.25	$172.25	$172.20
Purchase #5	$144.26	12.753%	$162.6575	$162.66	$162.65	$162.70
Purchase #6	$62.70	6.193%	$66.583	$66.58	$66.60	$66.60
Purchase #7	$134.86	7.645%	$145.17	$145.17	$145.15	$145.20
7 purchase totals =	$856.88		$934.4766	$934.48	$934.45	$934.50