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	$17.68	13.553%	$20.0762	$20.08	$20.10	$20.10
Purchase #2	$52.83	5.549%	$55.7615	$55.76	$55.75	$55.80
Purchase #3	$141.95	13.198%	$160.6846	$160.68	$160.70	$160.70
Purchase #4	$213.83	6.205%	$227.0982	$227.10	$227.10	$227.10
Purchase #5	$128.33	13.874%	$146.1345	$146.13	$146.15	$146.10
Purchase #6	$142.95	10.540%	$158.0169	$158.02	$158.00	$158.00
Purchase #7	$69.60	12.219%	$78.1044	$78.10	$78.10	$78.10
7 purchase totals =	$767.17		$845.8763	$845.87	$845.90	$845.90