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	$111.91	10.358%	$123.5016	$123.50	$123.50	$123.50
Purchase #2	$202.45	8.353%	$219.3606	$219.36	$219.35	$219.40
Purchase #3	$179.82	9.505%	$196.9119	$196.91	$196.90	$196.90
Purchase #4	$50.71	6.864%	$54.1907	$54.19	$54.20	$54.20
Purchase #5	$231.84	8.499%	$251.5441	$251.54	$251.55	$251.50
Purchase #6	$48.87	8.857%	$53.1984	$53.20	$53.20	$53.20
Purchase #7	$150.83	4.205%	$157.1724	$157.17	$157.15	$157.20
7 purchase totals =	$976.43		$1,055.8797	$1,055.87	$1,055.85	$1,055.90