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	$29.54	7.509%	$31.7582	$31.76	$31.75	$31.80
Purchase #2	$82.71	11.200%	$91.9735	$91.97	$91.95	$92.00
Purchase #3	$108.59	3.323%	$112.1984	$112.20	$112.20	$112.20
Purchase #4	$135.88	6.335%	$144.488	$144.49	$144.50	$144.50
Purchase #5	$49.96	11.262%	$55.5865	$55.59	$55.60	$55.60
Purchase #6	$29.89	7.407%	$32.104	$32.10	$32.10	$32.10
Purchase #7	$236.27	10.592%	$261.2957	$261.30	$261.30	$261.30
7 purchase totals =	$672.84		$729.4043	$729.41	$729.40	$729.50