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	$42.97	10.586%	$47.5188	$47.52	$47.50	$47.50
Purchase #2	$36.72	12.114%	$41.1683	$41.17	$41.15	$41.20
Purchase #3	$79.35	4.284%	$82.7494	$82.75	$82.75	$82.70
Purchase #4	$126.91	6.143%	$134.7061	$134.71	$134.70	$134.70
Purchase #5	$116.77	5.570%	$123.2741	$123.27	$123.25	$123.30
Purchase #6	$45.87	3.160%	$47.3195	$47.32	$47.30	$47.30
Purchase #7	$163.72	13.565%	$185.9286	$185.93	$185.95	$185.90
7 purchase totals =	$612.31		$662.6648	$662.67	$662.60	$662.60