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	$113.71	5.304%	$119.7412	$119.74	$119.75	$119.70
Purchase #2	$153.89	3.251%	$158.893	$158.89	$158.90	$158.90
Purchase #3	$79.79	3.869%	$82.8771	$82.88	$82.90	$82.90
Purchase #4	$197.68	6.548%	$210.6241	$210.62	$210.60	$210.60
Purchase #5	$133.43	3.397%	$137.9626	$137.96	$137.95	$138.00
Purchase #6	$201.70	10.858%	$223.6006	$223.60	$223.60	$223.60
Purchase #7	$62.61	4.325%	$65.3179	$65.32	$65.30	$65.30
7 purchase totals =	$942.81		$999.0165	$999.01	$999.00	$999.00