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	$6.88	10.340%	$7.5914	$7.59	$7.60	$7.60
Purchase #2	$96.27	3.373%	$99.5172	$99.52	$99.50	$99.50
Purchase #3	$220.31	9.612%	$241.4862	$241.49	$241.50	$241.50
Purchase #4	$39.71	8.280%	$42.998	$43.00	$43.00	$43.00
Purchase #5	$132.82	6.855%	$141.9248	$141.92	$141.90	$141.90
Purchase #6	$88.72	5.590%	$93.6794	$93.68	$93.70	$93.70
Purchase #7	$84.60	10.227%	$93.252	$93.25	$93.25	$93.30
7 purchase totals =	$669.31		$720.4490	$720.45	$720.45	$720.50