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	$111.32	13.429%	$126.2692	$126.27	$126.25	$126.30
Purchase #2	$196.34	6.391%	$208.8881	$208.89	$208.90	$208.90
Purchase #3	$118.55	7.369%	$127.2859	$127.29	$127.30	$127.30
Purchase #4	$118.35	3.531%	$122.5289	$122.53	$122.55	$122.50
Purchase #5	$69.39	9.373%	$75.8939	$75.89	$75.90	$75.90
Purchase #6	$64.91	3.826%	$67.3935	$67.39	$67.40	$67.40
Purchase #7	$97.80	9.728%	$107.314	$107.31	$107.30	$107.30
7 purchase totals =	$776.66		$835.5735	$835.57	$835.60	$835.60