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	$80.43	13.212%	$91.0564	$91.06	$91.05	$91.10
Purchase #2	$34.67	13.779%	$39.4472	$39.45	$39.45	$39.40
Purchase #3	$19.28	5.464%	$20.3335	$20.33	$20.35	$20.30
Purchase #4	$101.69	13.487%	$115.4049	$115.40	$115.40	$115.40
Purchase #5	$60.85	7.454%	$65.3858	$65.39	$65.40	$65.40
Purchase #6	$86.83	4.384%	$90.6366	$90.64	$90.65	$90.60
Purchase #7	$232.93	9.209%	$254.3805	$254.38	$254.40	$254.40
7 purchase totals =	$616.68		$676.6449	$676.65	$676.70	$676.60