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	$240.61	6.750%	$256.8512	$256.85	$256.85	$256.90
Purchase #2	$118.45	8.592%	$128.6272	$128.63	$128.65	$128.60
Purchase #3	$137.58	10.525%	$152.0603	$152.06	$152.05	$152.10
Purchase #4	$162.81	10.125%	$179.2945	$179.29	$179.30	$179.30
Purchase #5	$144.71	6.320%	$153.8557	$153.86	$153.85	$153.90
Purchase #6	$96.39	4.167%	$100.4066	$100.41	$100.40	$100.40
Purchase #7	$152.30	5.558%	$160.7648	$160.76	$160.75	$160.80
7 purchase totals =	$1,052.85		$1,131.8603	$1,131.86	$1,131.85	$1,132.00