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	$144.65	5.241%	$152.2311	$152.23	$152.25	$152.20
Purchase #2	$53.90	6.479%	$57.3922	$57.39	$57.40	$57.40
Purchase #3	$133.37	6.496%	$142.0337	$142.03	$142.05	$142.00
Purchase #4	$11.54	6.339%	$12.2715	$12.27	$12.25	$12.30
Purchase #5	$26.43	5.555%	$27.8982	$27.90	$27.90	$27.90
Purchase #6	$55.81	13.752%	$63.485	$63.49	$63.50	$63.50
Purchase #7	$191.91	9.829%	$210.7728	$210.77	$210.75	$210.80
7 purchase totals =	$617.61		$666.0845	$666.08	$666.10	$666.10