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	$21.65	10.396%	$23.9007	$23.90	$23.90	$23.90
Purchase #2	$106.52	6.613%	$113.5642	$113.56	$113.55	$113.60
Purchase #3	$184.27	3.154%	$190.0819	$190.08	$190.10	$190.10
Purchase #4	$29.68	6.639%	$31.6505	$31.65	$31.65	$31.70
Purchase #5	$64.88	10.374%	$71.6107	$71.61	$71.60	$71.60
Purchase #6	$145.95	11.443%	$162.6511	$162.65	$162.65	$162.70
Purchase #7	$167.55	11.802%	$187.3243	$187.32	$187.30	$187.30
7 purchase totals =	$720.50		$780.7834	$780.77	$780.75	$780.90