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	$110.66	5.553%	$116.8049	$116.80	$116.80	$116.80
Purchase #2	$100.61	11.758%	$112.4397	$112.44	$112.45	$112.40
Purchase #3	$86.75	9.268%	$94.79	$94.79	$94.80	$94.80
Purchase #4	$133.89	4.264%	$139.5991	$139.60	$139.60	$139.60
Purchase #5	$242.89	13.228%	$275.0195	$275.02	$275.00	$275.00
Purchase #6	$173.80	10.700%	$192.3966	$192.40	$192.40	$192.40
Purchase #7	$181.35	10.568%	$200.5151	$200.52	$200.50	$200.50
7 purchase totals =	$1,029.95		$1,131.5649	$1,131.57	$1,131.55	$1,131.50