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	$60.61	3.769%	$62.8944	$62.89	$62.90	$62.90
Purchase #2	$33.52	9.292%	$36.6347	$36.63	$36.65	$36.60
Purchase #3	$121.99	12.537%	$137.2839	$137.28	$137.30	$137.30
Purchase #4	$107.51	11.541%	$119.9177	$119.92	$119.90	$119.90
Purchase #5	$33.46	12.733%	$37.7205	$37.72	$37.70	$37.70
Purchase #6	$119.64	7.381%	$128.4706	$128.47	$128.45	$128.50
Purchase #7	$128.86	10.794%	$142.7691	$142.77	$142.75	$142.80
7 purchase totals =	$605.59		$665.6909	$665.68	$665.65	$665.70