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	$113.52	5.347%	$119.5899	$119.59	$119.60	$119.60
Purchase #2	$136.30	6.333%	$144.9319	$144.93	$144.95	$144.90
Purchase #3	$212.87	4.356%	$222.1426	$222.14	$222.15	$222.10
Purchase #4	$233.37	12.515%	$262.5763	$262.58	$262.60	$262.60
Purchase #5	$134.53	9.685%	$147.5592	$147.56	$147.55	$147.60
Purchase #6	$240.36	10.119%	$264.682	$264.68	$264.70	$264.70
Purchase #7	$113.45	13.401%	$128.6534	$128.65	$128.65	$128.70
7 purchase totals =	$1,184.40		$1,290.1353	$1,290.13	$1,290.20	$1,290.20