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	$39.69	4.782%	$41.588	$41.59	$41.60	$41.60
Purchase #2	$133.49	6.602%	$142.303	$142.30	$142.30	$142.30
Purchase #3	$219.96	12.126%	$246.6323	$246.63	$246.65	$246.60
Purchase #4	$132.32	7.712%	$142.5245	$142.52	$142.50	$142.50
Purchase #5	$152.68	7.576%	$164.247	$164.25	$164.25	$164.20
Purchase #6	$39.81	6.449%	$42.3773	$42.38	$42.40	$42.40
Purchase #7	$207.63	8.232%	$224.7221	$224.72	$224.70	$224.70
7 purchase totals =	$925.58		$1,004.3942	$1,004.39	$1,004.40	$1,004.30