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	$136.60	12.139%	$153.1819	$153.18	$153.20	$153.20
Purchase #2	$36.59	8.282%	$39.6204	$39.62	$39.60	$39.60
Purchase #3	$96.35	12.332%	$108.2319	$108.23	$108.25	$108.20
Purchase #4	$62.58	9.483%	$68.5145	$68.51	$68.50	$68.50
Purchase #5	$136.38	5.241%	$143.5277	$143.53	$143.55	$143.50
Purchase #6	$118.75	8.162%	$128.4424	$128.44	$128.45	$128.40
Purchase #7	$105.31	13.855%	$119.9007	$119.90	$119.90	$119.90
7 purchase totals =	$692.56		$761.4195	$761.41	$761.45	$761.30