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	$156.82	7.208%	$168.1236	$168.12	$168.10	$168.10
Purchase #2	$231.48	3.632%	$239.8874	$239.89	$239.90	$239.90
Purchase #3	$153.59	9.426%	$168.0674	$168.07	$168.05	$168.10
Purchase #4	$192.75	11.226%	$214.3881	$214.39	$214.40	$214.40
Purchase #5	$86.48	4.490%	$90.363	$90.36	$90.35	$90.40
Purchase #6	$114.41	9.509%	$125.2892	$125.29	$125.30	$125.30
Purchase #7	$128.63	10.860%	$142.5992	$142.60	$142.60	$142.60
7 purchase totals =	$1,064.16		$1,148.7179	$1,148.72	$1,148.70	$1,148.80