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	$42.31	10.367%	$46.6963	$46.70	$46.70	$46.70
Purchase #2	$152.66	7.771%	$164.5232	$164.52	$164.50	$164.50
Purchase #3	$83.95	9.784%	$92.1637	$92.16	$92.15	$92.20
Purchase #4	$136.72	7.723%	$147.2789	$147.28	$147.30	$147.30
Purchase #5	$46.62	13.487%	$52.9076	$52.91	$52.90	$52.90
Purchase #6	$62.78	12.651%	$70.7223	$70.72	$70.70	$70.70
Purchase #7	$51.34	9.528%	$56.2317	$56.23	$56.25	$56.20
7 purchase totals =	$576.38		$630.5237	$630.52	$630.50	$630.50