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	$115.51	11.583%	$128.8895	$128.89	$128.90	$128.90
Purchase #2	$135.47	4.462%	$141.5147	$141.51	$141.50	$141.50
Purchase #3	$141.82	8.240%	$153.506	$153.51	$153.50	$153.50
Purchase #4	$220.32	6.685%	$235.0484	$235.05	$235.05	$235.00
Purchase #5	$182.71	4.284%	$190.5373	$190.54	$190.55	$190.50
Purchase #6	$44.28	5.426%	$46.6826	$46.68	$46.70	$46.70
Purchase #7	$72.94	9.693%	$80.0101	$80.01	$80.00	$80.00
7 purchase totals =	$913.05		$976.1886	$976.19	$976.20	$976.10