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	$124.66	12.624%	$140.3971	$140.40	$140.40	$140.40
Purchase #2	$241.68	11.138%	$268.5983	$268.60	$268.60	$268.60
Purchase #3	$170.83	12.676%	$192.4844	$192.48	$192.50	$192.50
Purchase #4	$62.84	4.403%	$65.6068	$65.61	$65.60	$65.60
Purchase #5	$89.58	5.643%	$94.635	$94.64	$94.65	$94.60
Purchase #6	$188.30	4.389%	$196.5645	$196.56	$196.55	$196.60
Purchase #7	$144.81	8.632%	$157.31	$157.31	$157.30	$157.30
7 purchase totals =	$1,022.70		$1,115.5961	$1,115.60	$1,115.60	$1,115.60