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	$250.91	6.797%	$267.9644	$267.96	$267.95	$268.00
Purchase #2	$35.80	6.184%	$38.0139	$38.01	$38.00	$38.00
Purchase #3	$147.83	10.219%	$162.9367	$162.94	$162.95	$162.90
Purchase #4	$22.53	12.645%	$25.3789	$25.38	$25.40	$25.40
Purchase #5	$81.71	5.426%	$86.1436	$86.14	$86.15	$86.10
Purchase #6	$139.89	4.553%	$146.2592	$146.26	$146.25	$146.30
Purchase #7	$104.60	11.459%	$116.5861	$116.59	$116.60	$116.60
7 purchase totals =	$783.27		$843.2828	$843.28	$843.30	$843.30