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	$163.67	4.405%	$170.8797	$170.88	$170.90	$170.90
Purchase #2	$72.85	10.596%	$80.5692	$80.57	$80.55	$80.60
Purchase #3	$157.90	6.491%	$168.1493	$168.15	$168.15	$168.10
Purchase #4	$189.29	7.286%	$203.0817	$203.08	$203.10	$203.10
Purchase #5	$75.51	3.493%	$78.1476	$78.15	$78.15	$78.10
Purchase #6	$114.95	4.298%	$119.8906	$119.89	$119.90	$119.90
Purchase #7	$68.58	5.103%	$72.0796	$72.08	$72.10	$72.10
7 purchase totals =	$842.75		$892.7977	$892.80	$892.85	$892.80