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	$122.47	5.179%	$128.8127	$128.81	$128.80	$128.80
Purchase #2	$111.41	4.580%	$116.5126	$116.51	$116.50	$116.50
Purchase #3	$23.25	10.771%	$25.7543	$25.75	$25.75	$25.80
Purchase #4	$103.71	5.788%	$109.7127	$109.71	$109.70	$109.70
Purchase #5	$187.37	3.503%	$193.9336	$193.93	$193.95	$193.90
Purchase #6	$193.26	3.698%	$200.4068	$200.41	$200.40	$200.40
Purchase #7	$96.91	8.866%	$105.502	$105.50	$105.50	$105.50
7 purchase totals =	$838.38		$880.6347	$880.62	$880.60	$880.60