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	$137.31	11.352%	$152.8974	$152.90	$152.90	$152.90
Purchase #2	$128.85	11.153%	$143.2206	$143.22	$143.20	$143.20
Purchase #3	$74.96	7.401%	$80.5078	$80.51	$80.50	$80.50
Purchase #4	$5.65	13.473%	$6.4112	$6.41	$6.40	$6.40
Purchase #5	$103.26	7.572%	$111.0788	$111.08	$111.10	$111.10
Purchase #6	$49.43	9.440%	$54.0962	$54.10	$54.10	$54.10
Purchase #7	$79.66	9.653%	$87.3496	$87.35	$87.35	$87.30
7 purchase totals =	$579.12		$635.5616	$635.57	$635.55	$635.50