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	$229.68	11.588%	$256.2953	$256.30	$256.30	$256.30
Purchase #2	$51.58	10.337%	$56.9118	$56.91	$56.90	$56.90
Purchase #3	$99.88	13.137%	$113.0012	$113.00	$113.00	$113.00
Purchase #4	$94.64	9.541%	$103.6696	$103.67	$103.65	$103.70
Purchase #5	$136.47	8.824%	$148.5121	$148.51	$148.50	$148.50
Purchase #6	$144.79	7.263%	$155.3061	$155.31	$155.30	$155.30
Purchase #7	$236.28	12.786%	$266.4908	$266.49	$266.50	$266.50
7 purchase totals =	$993.32		$1,100.1869	$1,100.19	$1,100.15	$1,100.20