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	$150.32	9.650%	$164.8259	$164.83	$164.85	$164.80
Purchase #2	$216.76	12.835%	$244.5811	$244.58	$244.60	$244.60
Purchase #3	$182.51	12.141%	$204.6685	$204.67	$204.65	$204.70
Purchase #4	$85.25	9.527%	$93.3718	$93.37	$93.35	$93.40
Purchase #5	$227.99	9.236%	$249.0472	$249.05	$249.05	$249.00
Purchase #6	$63.32	3.609%	$65.6052	$65.61	$65.60	$65.60
Purchase #7	$112.85	13.354%	$127.92	$127.92	$127.90	$127.90
7 purchase totals =	$1,039.00		$1,150.0197	$1,150.03	$1,150.00	$1,150.00