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	$204.74	6.579%	$218.2098	$218.21	$218.20	$218.20
Purchase #2	$59.67	7.136%	$63.9281	$63.93	$63.95	$63.90
Purchase #3	$112.31	13.716%	$127.7144	$127.71	$127.70	$127.70
Purchase #4	$141.52	11.630%	$157.9788	$157.98	$158.00	$158.00
Purchase #5	$128.25	4.180%	$133.6109	$133.61	$133.60	$133.60
Purchase #6	$144.44	9.479%	$158.1315	$158.13	$158.15	$158.10
Purchase #7	$68.31	5.865%	$72.3164	$72.32	$72.30	$72.30
7 purchase totals =	$859.24		$931.8899	$931.89	$931.90	$931.80