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	$46.31	7.746%	$49.8972	$49.90	$49.90	$49.90
Purchase #2	$117.77	11.743%	$131.5997	$131.60	$131.60	$131.60
Purchase #3	$132.72	7.262%	$142.3581	$142.36	$142.35	$142.40
Purchase #4	$174.60	3.676%	$181.0183	$181.02	$181.00	$181.00
Purchase #5	$63.70	9.179%	$69.547	$69.55	$69.55	$69.50
Purchase #6	$103.27	4.702%	$108.1258	$108.13	$108.15	$108.10
Purchase #7	$138.52	11.148%	$153.9622	$153.96	$153.95	$154.00
7 purchase totals =	$776.89		$836.5083	$836.52	$836.50	$836.50