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	$160.59	3.848%	$166.7695	$166.77	$166.75	$166.80
Purchase #2	$122.72	11.240%	$136.5137	$136.51	$136.50	$136.50
Purchase #3	$155.44	11.113%	$172.714	$172.71	$172.70	$172.70
Purchase #4	$122.58	12.861%	$138.345	$138.35	$138.35	$138.30
Purchase #5	$92.26	4.219%	$96.1524	$96.15	$96.15	$96.20
Purchase #6	$248.81	12.587%	$280.1277	$280.13	$280.15	$280.10
Purchase #7	$47.85	6.302%	$50.8655	$50.87	$50.85	$50.90
7 purchase totals =	$950.25		$1,041.4878	$1,041.49	$1,041.45	$1,041.50