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	$150.43	10.112%	$165.6415	$165.64	$165.65	$165.60
Purchase #2	$139.32	8.662%	$151.3879	$151.39	$151.40	$151.40
Purchase #3	$193.70	7.660%	$208.5374	$208.54	$208.55	$208.50
Purchase #4	$142.29	9.250%	$155.4518	$155.45	$155.45	$155.50
Purchase #5	$210.61	6.395%	$224.0785	$224.08	$224.10	$224.10
Purchase #6	$131.75	10.407%	$145.4612	$145.46	$145.45	$145.50
Purchase #7	$241.28	8.700%	$262.2714	$262.27	$262.25	$262.30
7 purchase totals =	$1,209.38		$1,312.8297	$1,312.83	$1,312.85	$1,312.90