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	$250.72	8.774%	$272.7182	$272.72	$272.70	$272.70
Purchase #2	$169.43	12.394%	$190.4292	$190.43	$190.45	$190.40
Purchase #3	$25.60	8.681%	$27.8223	$27.82	$27.80	$27.80
Purchase #4	$228.57	13.401%	$259.2007	$259.20	$259.20	$259.20
Purchase #5	$76.47	5.373%	$80.5787	$80.58	$80.60	$80.60
Purchase #6	$184.37	8.194%	$199.4773	$199.48	$199.50	$199.50
Purchase #7	$228.85	11.668%	$255.5522	$255.55	$255.55	$255.60
7 purchase totals =	$1,164.01		$1,285.7786	$1,285.78	$1,285.80	$1,285.80