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	$111.73	13.838%	$127.1912	$127.19	$127.20	$127.20
Purchase #2	$136.79	12.446%	$153.8149	$153.81	$153.80	$153.80
Purchase #3	$98.85	13.448%	$112.1433	$112.14	$112.15	$112.10
Purchase #4	$246.88	4.801%	$258.7327	$258.73	$258.75	$258.70
Purchase #5	$98.53	7.183%	$105.6074	$105.61	$105.60	$105.60
Purchase #6	$169.69	5.683%	$179.3335	$179.33	$179.35	$179.30
Purchase #7	$56.64	8.600%	$61.511	$61.51	$61.50	$61.50
7 purchase totals =	$919.11		$998.3340	$998.32	$998.35	$998.20