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	$65.40	11.379%	$72.8419	$72.84	$72.85	$72.80
Purchase #2	$36.52	5.442%	$38.5074	$38.51	$38.50	$38.50
Purchase #3	$149.44	13.436%	$169.5188	$169.52	$169.50	$169.50
Purchase #4	$217.78	3.260%	$224.8796	$224.88	$224.90	$224.90
Purchase #5	$13.82	6.341%	$14.6963	$14.70	$14.70	$14.70
Purchase #6	$206.42	11.556%	$230.2739	$230.27	$230.25	$230.30
Purchase #7	$83.69	6.851%	$89.4236	$89.42	$89.40	$89.40
7 purchase totals =	$773.07		$840.1415	$840.14	$840.10	$840.10