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	$74.38	6.120%	$78.9321	$78.93	$78.95	$78.90
Purchase #2	$73.68	12.160%	$82.6395	$82.64	$82.65	$82.60
Purchase #3	$119.69	8.768%	$130.1844	$130.18	$130.20	$130.20
Purchase #4	$152.25	10.685%	$168.5179	$168.52	$168.50	$168.50
Purchase #5	$184.25	9.569%	$201.8809	$201.88	$201.90	$201.90
Purchase #6	$100.69	6.696%	$107.4322	$107.43	$107.45	$107.40
Purchase #7	$63.85	3.594%	$66.1448	$66.14	$66.15	$66.10
7 purchase totals =	$768.79		$835.7318	$835.72	$835.80	$835.60