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	$248.76	10.194%	$274.1186	$274.12	$274.10	$274.10
Purchase #2	$146.98	12.264%	$165.0056	$165.01	$165.00	$165.00
Purchase #3	$118.78	13.304%	$134.5825	$134.58	$134.60	$134.60
Purchase #4	$182.64	4.748%	$191.3117	$191.31	$191.30	$191.30
Purchase #5	$173.40	4.477%	$181.1631	$181.16	$181.15	$181.20
Purchase #6	$117.58	5.338%	$123.8564	$123.86	$123.85	$123.90
Purchase #7	$231.54	12.136%	$259.6397	$259.64	$259.65	$259.60
7 purchase totals =	$1,219.68		$1,329.6776	$1,329.68	$1,329.65	$1,329.70