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	$29.42	7.138%	$31.52	$31.52	$31.50	$31.50
Purchase #2	$84.85	6.280%	$90.1786	$90.18	$90.20	$90.20
Purchase #3	$217.91	7.755%	$234.8089	$234.81	$234.80	$234.80
Purchase #4	$106.54	4.388%	$111.215	$111.22	$111.20	$111.20
Purchase #5	$57.31	6.808%	$61.2117	$61.21	$61.20	$61.20
Purchase #6	$72.59	5.520%	$76.597	$76.60	$76.60	$76.60
Purchase #7	$51.35	10.273%	$56.6252	$56.63	$56.65	$56.60
7 purchase totals =	$619.97		$662.1564	$662.17	$662.15	$662.10