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	$94.27	9.357%	$103.0908	$103.09	$103.10	$103.10
Purchase #2	$54.55	7.389%	$58.5807	$58.58	$58.60	$58.60
Purchase #3	$96.40	6.869%	$103.0217	$103.02	$103.00	$103.00
Purchase #4	$39.40	7.273%	$42.2656	$42.27	$42.25	$42.30
Purchase #5	$59.29	8.104%	$64.0949	$64.09	$64.10	$64.10
Purchase #6	$167.32	9.564%	$183.3225	$183.32	$183.30	$183.30
Purchase #7	$132.66	4.713%	$138.9123	$138.91	$138.90	$138.90
7 purchase totals =	$643.89		$693.2885	$693.28	$693.25	$693.30