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	$227.76	13.499%	$258.5053	$258.51	$258.50	$258.50
Purchase #2	$105.37	8.843%	$114.6879	$114.69	$114.70	$114.70
Purchase #3	$99.89	13.408%	$113.2833	$113.28	$113.30	$113.30
Purchase #4	$48.89	5.582%	$51.619	$51.62	$51.60	$51.60
Purchase #5	$73.52	6.845%	$78.5524	$78.55	$78.55	$78.60
Purchase #6	$114.60	11.632%	$127.9303	$127.93	$127.95	$127.90
Purchase #7	$71.84	6.296%	$76.363	$76.36	$76.35	$76.40
7 purchase totals =	$741.87		$820.9412	$820.94	$820.95	$821.00