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	$24.25	11.703%	$27.088	$27.09	$27.10	$27.10
Purchase #2	$68.77	6.861%	$73.4883	$73.49	$73.50	$73.50
Purchase #3	$49.78	7.141%	$53.3348	$53.33	$53.35	$53.30
Purchase #4	$174.90	12.334%	$196.4722	$196.47	$196.45	$196.50
Purchase #5	$67.95	8.225%	$73.5389	$73.54	$73.55	$73.50
Purchase #6	$113.48	12.476%	$127.6378	$127.64	$127.65	$127.60
Purchase #7	$221.32	4.388%	$231.0315	$231.03	$231.05	$231.00
7 purchase totals =	$720.45		$782.5915	$782.59	$782.65	$782.50