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	$38.53	4.114%	$40.1151	$40.12	$40.10	$40.10
Purchase #2	$21.45	9.809%	$23.554	$23.55	$23.55	$23.60
Purchase #3	$178.62	6.712%	$190.609	$190.61	$190.60	$190.60
Purchase #4	$112.57	5.288%	$118.5227	$118.52	$118.50	$118.50
Purchase #5	$76.34	3.166%	$78.7569	$78.76	$78.75	$78.80
Purchase #6	$136.87	11.520%	$152.6374	$152.64	$152.65	$152.60
Purchase #7	$163.73	4.607%	$171.273	$171.27	$171.25	$171.30
7 purchase totals =	$728.11		$775.4681	$775.47	$775.40	$775.50