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	$55.36	5.444%	$58.3738	$58.37	$58.35	$58.40
Purchase #2	$193.38	13.131%	$218.7727	$218.77	$218.75	$218.80
Purchase #3	$228.55	4.449%	$238.7182	$238.72	$238.70	$238.70
Purchase #4	$206.71	7.462%	$222.1347	$222.13	$222.15	$222.10
Purchase #5	$215.82	6.536%	$229.926	$229.93	$229.95	$229.90
Purchase #6	$217.49	8.414%	$235.7896	$235.79	$235.80	$235.80
Purchase #7	$86.29	3.820%	$89.5863	$89.59	$89.60	$89.60
7 purchase totals =	$1,203.60		$1,293.3013	$1,293.30	$1,293.30	$1,293.30