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	$224.76	13.690%	$255.5296	$255.53	$255.55	$255.50
Purchase #2	$52.67	11.493%	$58.7234	$58.72	$58.70	$58.70
Purchase #3	$127.72	3.580%	$132.2924	$132.29	$132.30	$132.30
Purchase #4	$202.65	12.430%	$227.8394	$227.84	$227.85	$227.80
Purchase #5	$19.53	10.353%	$21.5519	$21.55	$21.55	$21.60
Purchase #6	$27.71	12.465%	$31.1641	$31.16	$31.15	$31.20
Purchase #7	$64.56	10.386%	$71.2652	$71.27	$71.25	$71.30
7 purchase totals =	$719.60		$798.3660	$798.36	$798.35	$798.40