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	$243.59	12.845%	$274.8791	$274.88	$274.90	$274.90
Purchase #2	$42.72	9.463%	$46.7626	$46.76	$46.75	$46.80
Purchase #3	$144.31	9.525%	$158.0555	$158.06	$158.05	$158.10
Purchase #4	$24.77	5.564%	$26.1482	$26.15	$26.15	$26.10
Purchase #5	$172.64	10.630%	$190.9916	$190.99	$191.00	$191.00
Purchase #6	$55.60	7.163%	$59.5826	$59.58	$59.60	$59.60
Purchase #7	$117.32	11.716%	$131.0652	$131.07	$131.05	$131.10
7 purchase totals =	$800.95		$887.4848	$887.49	$887.50	$887.60