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	$129.44	5.576%	$136.6576	$136.66	$136.65	$136.70
Purchase #2	$197.37	3.175%	$203.6365	$203.64	$203.65	$203.60
Purchase #3	$89.80	11.719%	$100.3237	$100.32	$100.30	$100.30
Purchase #4	$174.77	12.205%	$196.1007	$196.10	$196.10	$196.10
Purchase #5	$112.26	13.655%	$127.5891	$127.59	$127.60	$127.60
Purchase #6	$135.48	4.389%	$141.4262	$141.43	$141.45	$141.40
Purchase #7	$50.81	7.431%	$54.5857	$54.59	$54.60	$54.60
7 purchase totals =	$889.93		$960.3195	$960.33	$960.35	$960.30