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	$23.47	5.527%	$24.7672	$24.77	$24.75	$24.80
Purchase #2	$27.80	12.809%	$31.3609	$31.36	$31.35	$31.40
Purchase #3	$102.54	11.652%	$114.488	$114.49	$114.50	$114.50
Purchase #4	$66.75	9.217%	$72.9023	$72.90	$72.90	$72.90
Purchase #5	$209.77	10.128%	$231.0155	$231.02	$231.00	$231.00
Purchase #6	$47.88	11.534%	$53.4025	$53.40	$53.40	$53.40
Purchase #7	$158.82	8.647%	$172.5532	$172.55	$172.55	$172.60
7 purchase totals =	$637.03		$700.4896	$700.49	$700.45	$700.60