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	$135.77	4.358%	$141.6869	$141.69	$141.70	$141.70
Purchase #2	$97.58	11.316%	$108.6222	$108.62	$108.60	$108.60
Purchase #3	$222.40	11.555%	$248.0983	$248.10	$248.10	$248.10
Purchase #4	$122.25	11.534%	$136.3503	$136.35	$136.35	$136.40
Purchase #5	$216.36	3.800%	$224.5817	$224.58	$224.60	$224.60
Purchase #6	$104.89	6.384%	$111.5862	$111.59	$111.60	$111.60
Purchase #7	$117.43	9.353%	$128.4132	$128.41	$128.40	$128.40
7 purchase totals =	$1,016.68		$1,099.3388	$1,099.34	$1,099.35	$1,099.40