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	$101.39	7.646%	$109.1423	$109.14	$109.15	$109.10
Purchase #2	$193.52	6.165%	$205.4505	$205.45	$205.45	$205.50
Purchase #3	$121.91	12.162%	$136.7367	$136.74	$136.75	$136.70
Purchase #4	$51.60	7.461%	$55.4499	$55.45	$55.45	$55.40
Purchase #5	$11.73	9.493%	$12.8435	$12.84	$12.85	$12.80
Purchase #6	$83.55	7.299%	$89.6483	$89.65	$89.65	$89.60
Purchase #7	$185.77	13.874%	$211.5437	$211.54	$211.55	$211.50
7 purchase totals =	$749.47		$820.8149	$820.81	$820.85	$820.60