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	$203.43	9.565%	$222.8881	$222.89	$222.90	$222.90
Purchase #2	$225.56	11.726%	$252.0092	$252.01	$252.00	$252.00
Purchase #3	$155.27	8.688%	$168.7599	$168.76	$168.75	$168.80
Purchase #4	$189.55	13.504%	$215.1468	$215.15	$215.15	$215.10
Purchase #5	$141.99	7.610%	$152.7954	$152.80	$152.80	$152.80
Purchase #6	$165.25	6.863%	$176.5911	$176.59	$176.60	$176.60
Purchase #7	$73.59	13.658%	$83.6409	$83.64	$83.65	$83.60
7 purchase totals =	$1,154.64		$1,271.8314	$1,271.84	$1,271.85	$1,271.80